Introduction                       

The soft tissue envelope that surrounds the hip acts as a constraint that prevents the femoral head from subluxating or dislocating out of the acetabulum.1 Therefore, preservation and adequate balancing of these structures are important when a total hip replacement (THR) is performed. Postoperative pain in THRs that are well positioned and radiologically well-fixed are commonly caused by abductor malfunction and failure to achieve an optimum soft tissue balance.2 A proper soft tissue balance consists of restoration of the hip biomechanics by restoring the center of rotation (by reproducing the offset and limb length), implanting the component in optimum position, minimizing impingement and instability, and addressing soft tissue contractures around the hip.

 

Soft Tissue Balancing in Total Hip Replacement

 

Importance of Femoral Offset

 

The precise definition of femoral offset is varied but in simple terms, femoral offset has been defined as the perpendicular distance between the center of the femoral head and the line through the center of femoral canal (or attachment of the abductors).3 The hip joint functions effectively as a fulcrum between the body weight and the opposing hip abductors (Fig. 5.1).4,5 A dynamic equilibrium is developed with a goal of keeping the pelvis level and preventing a Trendelenburg lurch. The lever arm between the center of the femoral head and the abductor muscles ((B) in Fig. 5.1) is less than that between the center of the femoral head and body weight ((A) in Fig. 5.1), placing the abductor muscles at a mechanical disadvantage. Therefore, the abductors must generate a force ((M) in Fig. 5.1) that is larger than body weight ((W) in Fig. 5.1) for equilibrium. Studies have shown this can translate into higher joint-reaction forces ((R) in Fig. 5.1) in THR if the femoral offset is not restored.6 Clinically this can present as prevalence of limp with a Trendelenburg gait, fatigue and the need of walking aids.3,7 On the other hand, an increase in femoral offset increases the lever arm of the abductor muscles, thereby reducing the abductor muscle force required for normal gait. This minimizes the resultant reactive force across the hip joint and hence results in lower rates of polyethylene wear.8 The increase in the offset also improves the contractile efficiency of the abductors by increasing their resting length. Moreover, this lateralized position tends to decrease the prevalence of femoro-pelvic impingement while concomitantly improving the soft tissue tensioning and providing stability.3 Sir John Charnley4 recognized the importance of offset restoration decades ago and advocated medialization the cup, avoidance of the femoral component anteversion and restoration of the offset. In this regard, he acknowledged the importance of the femoral component neck-shaft angle. Initially, he sought a femoral

 

 

 

 

 

Total Hip Arthroplasty

 

Figure 5.1: The hip joint (red star) functions effectively as a fulcrum between the body weight (W) and the opposing hip abductors (M). The lever arm between the center of the femoral head and the abductor muscles (B) is less than that between the center of the femoral head and body weight (A), placing the abductor muscles at a mechanical disadvantage. R represents the resultant joint reaction force. ‘x’ and ‘y’ represent the respective vectors of the forces in horizontal and vertical directions

 

component with neck-shaft angle of 125°, but the femoral component fractured related to the first-generation metals used. Thus, he accepted a 135° neck-shaft angle with a diminished offset but used a trochanteric osteotomy to improve the offset.

 

 

There are several ways to increase the femoral offset in a prosthetic hip.3,9,10 As advocated by Charnley,4 trochanteric osteotomy with lateral and distal advancement increases the offset and provides a biomechanical advantage by laterally and distally advancing the point of insertion of the abductors. However, the procedure does not improve the range of motion or lessen the likelihood of impingement. Moreover, nonunion of the trochanter is a potential complication. Increasing the length of the femoral neck or head increases the offset but results in increase in the limb length, which may not be desirable in many cases. A prosthetic design that decreases the neck-shaft angle will increase the offset with improved abductor tension (Fig. 5.2), but will decrease the limb length. This design has intrinsic limitations due to increased torsional forces at the bend that tends to rotate the femoral component, especially with activities involving load transmission. Davey et al11 concluded that the strain at the bend increased in a liner fashion with increasing offset. Also, the increase in this axial torque is greater than the rate at which the abductor mechanism is enhanced. Theoretically, this

 

Figure 5.2: The implant on the right has a lower neck-shaft angle (block arrows) and thus an increased offset (A > B). However, the overall length of the limb is slightly decreased by decreasing the neck-shaft angle

 

 

Soft Tissue Balancing in Total Hip Replacement

 

can contribute to micromotion and can affect the bony in growth and longevity of both cemented and uncemented implants but this has not been confirmed in clinical studies or in vivo models, thus, supporting its use.12 The dual offset femoral components medialize the neck to increase the offset, without affecting the length.13 The use of modular ‘offset’ or ‘lateralized’ acetabular liners can increase the offset while preserving limb length. But as the center of rotation is also displaced laterally and inferiorly, it also increases the body weight lever arm, an undesirable outcome. The impact on the body weight lever arm is more than the improvement in the abductor lever arm as the latter depends on the angle of the line of displacement. Thus, the use of these liners is limited to situations of instability when the surgeon has already used the other methods to increase the offset. A lower-level neck resection and more distal femoral stem placement combined with a longer neck segment can lateralize the femoral shaft without lengthening the limb. However, longer heads with skirts should be avoided as they tend to increase impingement. The intraoperative assessment and reproduction of femoral offset has been described later in this chapter.

 

Limb         Length         Discrepancy                 

Limb-length discrepancy (LLD) is one of the most common causes of patient dissatisfaction after THR.14-23 It is also one of the most common reasons for litigation against orthopedic surgeons in the United States.14 LLD is common after THA with reported average discrepancy between 3-16 mm.16,18 Generally LLD is well tolerated with only 1/3rd of patients noticing the difference and only half of these finding it bothersome. The boundary between acceptable and unacceptable levels of LLD still remains undefined. However, a true LLD of more than

1.5 cm may be a cause of concern as it can cause functional impairment (abductor weakness), back pain, hip pain, early fatigue, awkward gait, imbalance, sciatica, numbness, instability, aseptic loosening and occasionally revision surgery.14-23 When the limb is lengthened 4 cm, significant nerve injury may be seen in upto 28 percent of patients.23 Edwards et al23 noted an average lengthening of 2.7 cm (range 1.9 to 3.7 cm) for peroneal nerve palsy and 4.4 cm (range 4.0 to 5.1 cm) for sciatic nerve palsy.

 

PREOPERATIVE EVALUATION

Appropriate history and physical examination, radiographic evaluation, preoperative templating and intraoperative measurements can be used to identify those patients at risk for developing a LLD, and has been discussed in detail in previous chapter on preoperative planning (Chapter 3). Certain conditions may predispose to postoperative LLD and include coxa vara, dysplastic hips, protrusio, flexion contractures, fixed pelvic tilts, spinal deformities, neuromuscular disorders, hypermobile joints, short stature and preoperative longer limb, and hence, these patients need more detailed counseling. It is essential that the surgeon and the patient align their goals and expectations. Realistic expectations of the patients should be thoroughly discussed. It should be clarified that the primary goal is to achieve initial fixation with stability and the patient must understand and accept that some lengthening may be required to achieve this. The patient must also be told that they may have a functional lengthening after their surgery and this is normal.19 The patient should be counseled that the goal of the surgery is to attempt equalize the true length and not necessarily the functional length. Accordingly, as a component of obtaining informed consent, it is imperative that the surgeon discuss the potential of LLD. The assessment and correction of LLD intraoperative has been described later in this chapter.

 

POSTOPERATIVE ASSESSMENT AND TREATMENT OF LLD

If an unacceptable real LLD occurs postoperatively, it is imperative to recognize it and treat it appropriately. Postoperative assessment and classification of LLD (e.g. true and functional, direct and indirect), and the various indications and options for treatment have been

 

 

 

Total Hip Arthroplasty

 

described in detail elsewhere, and are beyond the scope of this chapter.16-19 The options include shoe lift on the contralateral side or shortening the operated side by using stems with an increased offset, using smaller modular implants, component repositioning, medializing or superiorizing the hip center, using offset acetabular liners, performing trochanteric osteotomies or using constrained liners to achieve stability. If the hip is stable and functions well, a distal femoral osteotomy is another option to correct the LLD. It cannot be overemphasized that all surgical options regarding limb shortening should be undertaken cautiously with adequate counseling because of the unpredictable nature of the procedure, the variable response, and the high complication rate.16-19

 

Component Positioning, Impingement and Instability     

POSITIONING OF THE COMPONENTS

Implant malposition is a major contributor to instability, dislocation, impingement, accelerated wear and failure of the THR.10,16,24,25 Significant changes in pelvic orientation and position occurs during the lateral position intraoperatively.25 Fixed bony landmarks are independent of patient positioning, in contrast to external aiming devices, and should be used during surgery to assist with the positioning of the components. Useful landmarks include transverse ligaments, distal tear drop (most distal and medial part of the acetabulum, behind the transverse ligament and at the superior border of the obturator foramen), infracotyloid groove, lateral pubis, superior ischium, superolateral acetabulum, lesser trochanter (LT), greater trochanter (GT), center of femoral head (CFR) and the saddle of the neck. Computer navigation may aid in identification of these landmarks.26 Although it reduces outliers, it is still evolving and it is cost and technical aspect prohibits its widespread use.

Multiple investigators have attempted to define a ‘safe zone’ of the acetabular component anteversion and inclination, which is around 40° + 10° and 15° + 10° respectively when used in combination with a cemented stem in 10° to 15° of anteversion.27 This requires medialization or superior displacement of the acetabular center of rotation. Moving the center of rotation in and/or up results in cup coverage that prevents metal neck-on-cup impingement, but it can reduce the length and offset of the hip, causing bone-on-bone impingement. The solutions for these problems are a higher osseous femoral neck cut, a longer modular head, a high-offset stem, or a combination of these.24,26 The concept of using combined anteversion (the sum of femoral and acetabular anteversion), rather than the target values, to determine the cup position when mating it with the stem is becoming more prevalent and has been recommended as 25° to 35° for men and 35° to 45° for women.24,28,29 Using a computed tomographic scans to assess component position, Komeno et al30 found that cases with anterior dislocation had significantly (p < 0.05) more combined anteversion (mean 72.2°) and cases with posterior dislocation had significantly less anteversion (mean 27.4°) than non-dislocators (mean 47.8°). The authors concluded that the dislocation rate is not affected by the positioning of either the cup or the stem alone but is influenced by the combined anteversion. Surgeons who use the anterior approach for arthroplasty have always recommended less cup anteversion. It has been shown that for the cementless component, the femoral anteversion is not under the surgeon’s control.24,31 The acetabular cup, when used with a cementless femoral stem, should be positioned in relation to the stem position (to achieve a target combined anteversion) rather than individual target values. Thus, some surgeons advocate preparing the femur first (rather than the conventional acetabulum first technique) to have an estimate of the femoral anteversion so that, the cup may be implanted in a position to achieve the target combined anteversion.24,26

Protrusio acetabuli, defined as medial migration of the head beyond the ilioischial line (Kohler’s line), may be present in inflammatory arthritis, osteoporosis, metabolic bone disease and post-trauma. Careful reaming is warranted in these cases as usually bone is also softer. Relative lateralization of the cup will be needed to restore the biomechanics and

 

 

 

Soft Tissue Balancing in Total Hip Replacement

 

minimize impingement (Chapter 3).32,33 Peripheral rim contact with supplementary screw fixation is desirable in these cases for primary stability. In most cases, bone graft from the femoral head would be sufficient, but severe cases may need structural allografts or cages. If lateralization increases the leg length, a shortened neck with a low neck cut may be needed. Moreover, asymmetric correction may have cosmetic implications, especially in females. In contrast, in cases of dysplastic hips with less superolateral covering, overmedialization with or without superior placement of a smaller size cup may be necessary (Chapter 3). A relative vertical cup with offset liner in superior position is another option. Structural grafts with metal augments may be necessary in some cases. Similarly in cases of hypertrophic osteoarthritis, it is important to adequately ream the medial osteophytes and medialize the cup with adequate superolateral coverage.

Deciding the level of femoral cut and reproduction of the femoral offset are critical for stability, impingement and optimizing the limb length. However, over correction should be avoided as it can lead to a symmetry, trochanteric prominence and bursitis. Cases with coxa vara are at increased risk for limb lengthening without restoring the offset.32,33 Options include lowering the neck cut and using a longer neck or using a higher offset (less neck shaft angle) prosthesis (Fig. 5.2). The opposite holds true for valgus hips. Similarly in cases of short neck (coxa brevia, e.g. in Perthes disease), a shorter neck cut with a shorter neck length is required. In doubtful cases, it is better to cut the neck longer and then adjust later on after trial reduction.

 

IMPINGEMENT

Impingement is a cause of poor outcomes of a THR and can lead to instability, accelerated wear, decreased range of motion, and unexplained pain.24,31,34-39 Impingement is influenced by prosthetic design, component position, biomechanical factors, and patient variables.24,31,34-39 A prosthetic head-neck ratio of <2.0 seems to greatly increase the risk of impingement. The head-neck ratio is influenced by the head size, the femoral neck geometry, and the use of a skirt on the femoral head. The use of a large femoral head ensures an acceptable head-neck ratio, even with a circular femoral neck. The large head provides a margin of error of combined anteversion for stability, but it may not reduce the margin of error for wear, which requires inclination of <45°.38 Features that increase acetabular impingement include the geometry of the rim of the polyethylene, presence of considerable osteophytes, and the presence of an extended-rim liner, particularly if the hood is incorrectly positioned in the hip. If a hood is used in an operation performed through a posterior approach, its apex should be placed posteroinferiorly (in the 4 o’clock position in left hips and in the 8 o’clock position in right hips), as the most frequent site of impingement is posterosuperior.24,37 The surgeon controls the positioning of the prosthesis and thus an optimal limb length, offset and soft tissue reconstruction will minimize the occurrence of impingement. Patient factors include a hyperflexible person and those cases in which there is a substantial change in pelvic tilt during activities (dynamic) as compared to static tilt on the operating table. These patients may impinge even with an ideal biomechanical reconstruction and use of a larger head has been recommended in these cases.24,26 Soft tissue impingement can be a source of pain in patients with a THR.24,39A large acetabular component overhanging medially or anteriorly, an overtly large femoral head, or the impingement of the lesser trochanter (LT) with the ischium can cause iliopsoas tendonitis. Similarly the capsule can impinge between the metal neck and the cup, or the greater trochanter (GT) and the ilium.

 

INSTABILITY

A recent study revealed that instability/dislocation was the most common diagnosis resulting in revision THA in the United States.40 The incidence varies from 0.2-7% after a primary THA and 10-25% after revision THA, and the cumulative risk increases over time.10,25,27,30,34,41,21 An understanding of the risk factors will help minimizing the incidence of instability. Patient-

 

 

Total Hip Arthroplasty

 

specific risk factors include female gender, older age, osteonecrosis, femoral neck fracture, dysplasia, prior surgery, obesity, a high preoperative range of motion, neuromuscular disorders and comorbidities, alcoholics and noncompliant patient. Similarly the surgical variables include surgical approach, component design, position and orientation, femoral head size, offset, preservation of soft tissue integrity, limb lengths, impingement, and experience and case volume of the surgeon. Evaluation, classification and treatment of instability has been described before10,25,27,30,34,41,42 and is beyond the scope of this chapter. Intraoperative assessment of stability has been discussed later in this chapter.

 

Role      of      Surgical      Approach                 

Choosing an appropriate surgical approach is a critical aspect of preoperative planning.43 Although most primary THRs can be done through the same approach based on the surgeon’s training, experience and level of comfort, certain approaches may have added benefit based on the information gathered during the preoperative evaluation as discussed in Chapter 3. The surgeon should be familiar with the advantages and disadvantages of the various surgical approaches43 and their implications in achieving stability and limb length equality. The advantage of a direct anterior approach is the ability to directly measure the true length as the patient is supine. Also, the dislocation rates have been reported to be lower than other approaches.44-45 However, it may require use of special table and intraoperative fluoroscopy. The lateral cutaneous nerve of the thigh is the structure at risk. There is also a steep learning curve for this approach. The direct lateral or anterolateral approaches may be performed in supine or lateral position. Approaches that dislocate the hip anteriorly during surgery have lower dislocation rates than those that dislocate the hip posteriorly during surgery. Since the direct lateral or anterolateral approaches appear relatively more stable, slight laxity to equalize the limb length is acceptable. The disadvantages include violation of abductor mechanism, risk to superior gluteal nerve and increased incidence of heterotrophic ossification. The posterior or posterolateral approach is the most extensile of all and is the most common approach in the United States. Intraoperative measurement of limb length is relatively difficult and several indirect methods have been described as mentioned later. The risk of dislocation is higher with this approach and because of this concern, it is not uncommon to lengthen these hips for stability. The other risk of this approach is the injury to sciatic nerve (0.6%).23

Berry et al45 reported a 3.1%, 3.4% and 6.9% dislocation rates over 10 years for anterolateral, transtrochanteric and posterolateral approaches respectively. A large meta-analysis on 13,203 primary THA reported dislocation rates as 1.27% for transtrochanteric, 3.23% for posterior (2.03% with posterior capsular repair), 2.18% for anterolateral, and 0.55% for the direct lateral approach.45 Repair of the posterior capsule and external rotators along with use of bigger heads reduces this complication.46 However, larger head increase the volumetric wear and thinner polyethylene liners are needed to accommodate them. To counter this, offset liners are offered by some implant manufacturers. Although the offset is increased, this is detrimental to overall biomechanics as discussed before. Trochanteric nonunion and/or abductor dysfunction can increase the dislocation rates by up to 6 fold.47

 

Release          of          Contractures                  

Release of static and dynamic contractures around the hip decreases postoperative knee and groin pain, increases the range of motion, reduces the functional LLD and accelerates postoperative rehabilitation.2,26 Following a meticulous preoperative plan (as described in Chapter 3), the surgeon should anticipate the necessity and need for soft tissue releases, when the patient presents with contractures of the hip that are more than 20° in flexion, abduction, or external rotation. Contractures should also be anticipated when the radiographs show substantial shortening. During surgery, tightness of the hip through the range of motion with the trial components in place indicates the necessity for soft tissue release. Failure to

 

 

bring the hip to full extension, failure to be able to abduct the hip beyond 20°, and failure to bend the knee beyond 90° to 100 ° (without knee arthritis or previous total knee arthroplasty) are indicative of soft tissues imbalance. However, it should be made sure that the tightness is not due to excessive overlengthening of the limb. Patients with adductor contracture may need percutaneous surgical release before the actual THR procedure.

 

Soft Tissue Balancing in Total Hip Replacement

 

FLEXION CONTRACTURE

If the hip does not extend beyond neutral, the surgeon must palpate the anterior capsule (static) and the iliopsoas tendon (dynamic). The other test is to log roll the leg back in extension. The posterior border of greater trochanter should be within one finger breadth from the ischial tuberosity without impinging. If needed, the tight capsule structure must be released to allow the hip to extend to at least 10°. A tight iliopsoas tendon can cause groin pain after surgery from irritation of the tendon as it crosses the anterior acetabulum.39 The ilio-psoas tendon must be recessed or completely released until it is elastic, as it is palpated in extension. However, if the iliopsoas tendon is completely released from the lesser trochanter, some patients may complain of weakness with ascent of stairs and lifting the leg to get in and out of a car or bed.

 

ABDUCTION AND EXTERNAL ROTATION CONTRACTURE

If the hip is very tight in abduction and external rotation (a positive Ober’s sign), release of the tensor fascia/iliotibial band becomes necessary. This is done by holding the tensor fascia with Kocher clamps just distal to the fascial band to the gluteus medius. The vastus lateralis is retracted and the tensor fascia is lifted anteriorly and divided. The tensorfascia can be divided completely to the rectus femor is muscle. The division of the tensor fascia muscle will allow improved abduction and external rotation of the hip.

 

INABILITY TO FLEX THE KNEE

If the knee does not flex beyond 90° to 100° even after releasing the tensor fascia, then the rectus tendon should be released. The rectus muscle can be brought into direct view by retracting the cut edges of the tensor fascia and the vastus lateralis. The rectus muscle can then be grasped and pulled into the wound and divided as necessary to allow the knee to flex further without resistance. This will also decrease the incidence of postoperative knee pain.

 

Intraoperative Assessment of Offset, Limb Length Discrepancy, Impingement, Stability and Soft Tissue Tension        

Because determining these variables intraoperatively relies on identifying anatomic landmarks, patient positioning and its assessment before prepping and draping is crucial. The relative position of the knees and feet with symmetrical flexion of the hips and knees can provide an idea about the starting leg length relationship. Usually the superior side on the lateral position would normally appear slightly shorter because of the adduction. Some surgeons prefer to palpate the knee and ankle intraoperatively and compare it side by side to the contralateral side for assessment of LLD. But the accuracy of this technique depends upon the patient’s position, the limb’s position, pelvic tilt, the effect of the drapes and the accessibility to the knees and feet.

Several intraoperative methods have been described to assess the biomechanical reconstruction during THR.18,20,26,48-54 Typically, all of these techniques are performed with the trial components and provide the surgeon the flexibility to adjust length or offset by using various combinations of sizes and designs to obtain an optimal clinical result. A variety of measuring calipers has been described in which one end articulates with a pin, screw, or

 

 

 

 

Total Hip Arthroplasty

 

Figure 5.3: A model of the hip joint showing the insertion of the 9/16 inch Steinmann pin in the posterior infracotyloid groove (white arrows), a bony landmark inferior to the posteroinferior hip of the acetabulum. The position of the Steinmann pin relative to the femur is marked (red arrow)

 

 

spike anchored into the pelvis, while a stylus references off a mark on the greater trochanter.48-54 The accuracy of all these methods may be affected by the inherent variability of the leg’s position when the measurements are made. Pin bending or dislodgement of a pin is another frequent problem.

 

AUTHORS’ PREFERRED METHOD

A thorough preoperative evaluation and planning is done as described in Chapter 3. We prefer the method described by Ranawat et al.18,20 This technique has been described using the posterior approach with a lateral position. After initial dissection and release of the short external rotators, the inferior capsule is incised at the 6 o’clock position to expose the posteroinferior lip of the acetabulum. A 9/16 inch Steinmann pin is inserted into the posterior infracotyloid groove (Figs 5.3 to 5.5). This represents the bony groove inferior to the posteroinferior hip of the acetabulum. The advantage of using this landmark is the close proximity of the pin to the center of rotation of the hip. The pin is placed initially at an angle of approximately 60° until it touches the ischium and then made vertical and allowed to

 

 

 

Figure 5.4: Intraoperative photograph showing the insertion of the 9/16 inch Steinmann pin in the posterior infracotyloid groove and marking its relative position on the femur (arrow) before dislocating the joint. GT: Greater trochanter; H: Femoral head; *: External rotators and posterior capsule of the hip joint

 

 

 

 

Soft Tissue Balancing in Total Hip Replacement

 

Figure 5.5: Intraoperative photograph showing the marking on the femur (arrow) after removal of the Steinmann pin. This mark will be used later for comparison of the limb length. GT: Greater trochanter; H: Femoral head; *: External rotators and posterior capsule of the hip joint

 

 

 

Figure 5.6: Intraoperative photograph showing the measurement (blue arrow) of the distance between the lesser trochanter (LT) and the center of femoral head (CFH) after dislocation of the joint. This is an intraoperative measurement of the limb length. GT: Greater trochanter

 

slide along the bone into the infracotyloid groove. Keeping the pin vertical and viewing it end-on from above, a mark on the GT is made prior to hip dislocation. The hip is then dislocated. The CFH is marked with electrocautery, and its distance from the LT and GT (usually from the saddle of the neck) (offset) is noted and compared to the assessment done during preoperative templating (Figs 5.6 and 5.7). The neck resection is now completed based on preoperative templating.

After bone preparation and placement of the trial implants, the distance from the CFH to the LT and CFH to the GT (offset) are reassessed and compared with the pre-neck-resection numbers (Figs 5.8 and 5.9). After trial reduction, the component position is assessed using the combined anteversion test (Fig. 5.10).18,20,28 This test measures the angle of internal rotation required for the femoral head to be coplanar with the face of the acetabulum with 10° of flexion and 10° of adduction.

Assuming the components are in proper position, attention is turned to the soft tissue envelope. Tightness of the tensor fascia lata is assessed by direct palpation and the Ober’s test (Fig. 5.11). Tightness of the anterior capsule is evaluated by keeping the leg in full extension

 

 

 

 

 

 

Total Hip Arthroplasty

 

Figure 5.7: Intraoperative photograph showing the measurement (blue arrow) of the distance between the saddle of the neck (S) and the center of femoral head (CFH) after dislocation of the joint. This is an intraoperative measurement of the offset. The saddle is the junction of the femoral neck and GT, usually at the piriformis fossa and is a more reproducible landmark. GT: Greater trochanter; LT: Lesser trochanter

 

 

 

Figure 5.8: Intraoperative photograph showing the measurement (blue arrow) of the distance between the lesser trochanter (LT) and the center of the trial prosthetic head (CPH). This is compared to the earlier distance for assessment of the limb length discrepancy (Fig. 5.6). GT: Greater trochanter

 

Figure 5.9: Intraoperative photograph showing the measurement (blue arrow) of the distance between the saddle of the neck (S) and the center of trial prosthetic head (CPH). This is compared to the earlier distance for assessment of the offset (Fig. 5.7). GT: Greater trochanter; LT: Lesser trochanter

 

 

 

 

 

 

Soft Tissue Balancing in Total Hip Replacement

 

Figure 5.10: Intraoperative photograph showing the clinical combined anteversion test. This test measures the angle (blue arrow) of internal rotation required for the femoral head to be coplanar within the cup (red arrows, inset) with about 10° of flexion and 10° of adduction at the hip

 

Figure 5.11: Intraoperative photograph showing the Ober’s test. Once the pelvis is stabilized, the hip is extended and circumducted, and slowly lowered towards the bottom limb. The test result is positive if the adduction beyond neutral is not possible and the thigh hangs in the air. In this case, the thigh is easily adducted towards the bottom limb (negative Ober’s test)

 

and externally rotating the hip (Fig. 5.12). The posterior border of greater trochanter should be within one finger breadth from the ischial tuberosity without impinging. The ‘shuck test’ can be used to determine overall laxity (Fig. 5.13).3,9,18 In general, more than half of the femoral head should not disengage from the liner with direct axial traction. The ‘drop kick test’ is a maneuver where the hip is held in extension while the knee is concomitantly flexed to 90° (Fig. 5.14).3,9 If the extremity has been over lengthened, the extensor mechanism becomes excessively taut and may manifest as passive swing of the knee into extension as the leg is released. Once adequate soft tissue balance is achieved around the hip, the Steinmann pin is re-inserted, keeping the pin and the leg in the same position (Fig. 5.15). The difference in the leg length is measured by noting whether the point on the trochanter has moved up or down indicating shortening or lengthening respectively.

Assessment is also performed for bone-bone, metal-metal and bone-metal impingement (Figs 5.16 A to D). Offset can also be determined by palpation of the interval between the greater trochanter and the pelvis during range of motion, and clinically there should be a gap of at least one finger breadth.2,26 Once the contractures are released, and the offset and limb length are optimized, there should be no impingement. The LT should not impinge with the

 

 

 

 

 

Total Hip Arthroplasty

 

Figure 5.12: Intraoperative photograph showing the evaluation of tightness of the anterior capsule. The hip is kept in neutral position with the knees extended and then the leg is externally rotated (green arrow, inset).The posterior border of greater trochanter should be within one finger breadth from the ischial tuberosity without impinging and should thus not crush the finger between the bones (blue arrow)

 

 

 

 

 

Figure 5.13: Intraoperative photograph showing the ‘shuck test’. In general, not more than half of the femoral head should disengage from the liner (blue arrow) with direct axial traction (white arrow)

 

Figure 5.14: Intraoperative photograph showing the ‘drop kick test’ maneuver. The hip is held in extension while the knee is concomitantly flexed to 90°. If the extremity has been overlengthened, the extensor mechanism becomes excessively taut and may manifest as passive swing of the knee into extension as the leg is released (blue arrow)

 

 

 

 

Soft Tissue Balancing in Total Hip Replacement

 

Figure 5.15: Intraoperative photograph showing the re-placement of the Steinmann pin after trial reduction. Note the lengthening (yellow arrow) when comparing the new position of the Steinmann pin with the previous one (black solid arrow) as shown in Figures 5.3 and 5.4

 

 

 

Figures 5.16A to D: Intraoperative photographs showing the assessment of impingement and stability at various range of motion at the hip. (A) Flexion with internal rotation. (B) Flexion with external rotation. (C) Extension with external rotation. (D) Extension with internal rotation

 

ischium with the lower limb in full extension; it should be proximal to the tip of the ischium by at least one finger breadth (the proper relationship can be determined from the preoperative radiograph if a normal contralateral hip is available for imaging). The GT should not impinge on the ilium in external rotation and abduction, or in flexion, adduction, and internal rotation. All anterior acetabular osteophytes must be removed. The prosthetic femoral

 

 

neck should not impinge with the rim of the cup at physiologic range of motion. If this cannot be done, the offset may not be appropriate and increase in neck/head size may be necessary. If leg length is correct and the implants seem reasonably placed but there is an impingement or instability, then a decision to increase the leg length, use a high/dual offset implant, lateralized polyethylene or to transfer the GT may need to be made.

Total Hip Arthroplasty

 

Using this method, Ranawat et al20 showed good correlation between the intraoperative measurements and the postoperative radiographic measurements (r = 0.84), with a mean postoperative LLD of 2.6 mm (–7 to +9 mm) in a series of 100 consecutive primary total hip arthroplasties. Shortcomings of this method include in accurate placement of the pin for any reason, e.g. presence of large osteophytes at the posteroinferior lip of the acetabulum, variability in determining vertical pin position or failure to identify the infracotyloid notch. The main advantage of this technique is that it is simple, accurate, and reproducible. The proximity of location of the pin at the infracotyloid groove to the center of rotation of the hip reduces the error in measurement caused by position of the limb and takes into consideration the location of the acetabular component.

During surgery if there is any doubt, a radiograph should be taken in the operating room, although some prefer to obtain it routinely. If lengthening of the limb is anticipated, especially more than 2 cm, the sciatic nerve must be palpated to determine whether it is excessively taut before accepting the length gained. Rarely, the use of more objective tests like somatosensory evoked potential monitoring is necessary to avoid this complication.

It should be emphasized that all these soft tissue tension tests are subjective and depend on the muscle relaxation at that point in the operation, the amount of effective force applied to distract the joint, the muscularity and habitus of the patient and the extent of soft tissue release conducted during surgery. Moreover, as these tests provide an assessment of stability, they may sometimes encourage increased neck lengths leading to potential limb lengthening.16 Thus, these tests should be used in conjunction with each other along with the preoperative template to determine the appropriate construct. In a retrospective study of 132 patients (63 spinal anesthesia and 69 general anesthesia) undergoing THR, LLD occurred in 87.0% of patients who received regional anesthesia as opposed to 47.6% patients who had general anesthesia (p < 0.001).55 Differences in postoperative medial offset was not statistically significant. The assumed reason was a denser motor blockade with regional anesthesia leading to more intraoperative laxity. This was more pronounced with the ‘shuck test’. In a prospective study using ‘shuck test’ or a caliper for intraoperative assessment of LLD, significantly greater variability was found in the ‘shuck test’ group using a cutoff of 0.5 cm.53 The authors concluded that the ‘shuck test’ was more indicative of the soft tissue balance rather than the leg length.

 

Future                       Trends                      

Advances in technology, especially with computed navigation, robotic surgery and simulation techniques will lead to greater precision and accuracy in limb length management.26,56,57 Accurate registration of three-dimensional bony anatomy, coupled with real time tracking during surgery, will allow the desired biomechanical reconstruction with optimal component placement with adequate soft tissue balance to ensure optimal clinical outcome.

 

Conclusion

 

Several basic principles must be considered for restoring the biomechanics of the THR. These include preoperative templating, establishment of anatomic center of rotation, intraoperative determinations of component positioning, limb length and femoral offset, and a thorough understanding of the various intraoperative options and clinical tests that can be employed to achieve optimum soft tissue balancing during THR. It is important to note that, under all circumstances, the establishment of hip stability must take precedence

 

 

 

Soft Tissue Balancing in Total Hip Replacement

 

over equalization of limb lengths and restoration of femoral offset, and its implications should be discussed with the patient preoperatively.

 

References                       

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2. Longjohn D, Dorr LD. Soft tissue balance of the hip. J Arthroplasty 1998;13(1):97-100.

3. Charles MN, Bourne RB, Davey JR, Greenwald AS, Morrey BF, Rorabeck CH. Soft-tissue balancing of the hip: the role of femoral offset restoration. Instr Course Lect 2005;54:131-41.

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6. Greenwald AS. Biomechanical factors in THR offset restoration. Presented as an instructional course lecture at the Annual Meeting of the American Academy of Orthopaedic Surgeons 2003; 5-9; New Orleans, LA.

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10. Berend KR, Sporer SM, Sierra RJ, Glassman AH, Morris MJ. Achieving stability and lower-limb length in total hip arthroplasty. J Bone Joint Surg Am 2010;92(16):2737-52.

11. Davey J, O’Connor D, Burke DW. Femoral component offset: its effect on micromotion strain in the cement, bone, and prosthesis. Orthop Trans 1989;13:566.

12. Wong P, Otsuka N, Davey JR, Fornasier VL, Binnington AG. The effect of femoral component offset in uncemented total hip arthroplasty. Read at the Annual Meeting of the Canadian Orthopaedic Association; 1993;31: Montreal, Quebec, Canada.

13. Dolhain P, Tsigaras H, Bourne RB, Rorabeck CH, MacDonald S, McCalden R. The effectiveness of dual offset stems in restoring offset during total hip replacement. Acta Orthop Belg 2002;68(5): 490-9.

14. Hofmann AA, Skrzynski MC. Leg-length inequality and nerve palsy in total hip arthroplasty: a lawyer awaits! Orthopedics 2000;23(9):943-4.

15. Clark CR, Huddleston HD, Schoch EP 3rd, Thomas BJ. Leg-length discrepancy after total hip arthroplasty. J Am Acad Orthop Surg 2006;14(1):38-45.

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17. Pritchett J. Nerve Injury and Limb Lengthening After Hip Replacement:

    Soft Tissue Balancing in

    Total Hip Replacement

    Treatment by shortening. Clin Orthop Relat Res 2004;418:168-71.

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19. Ranawat CS, Rodriguez JA. Functional Leg-length Inequality Following Total Hip Arthroplasty. J Arthroplasty 1997;12(4):359-64.

20. Ranawat CS, Rao RR, Rodriguez JA, Bhende HS. Correction of limb length inequality during total hip arthroplasty. J Arthroplasty