The Collum Femoris Preserving (CFP) Prosthesis in Primary Total Hip Replacement
Introduction
For the possible concept of anatomical primary hip replacement various types of prosthesis have been described within the last decades. One possible solution is provided by the concept of preserving the femoral neck as much as possible for the uncemented total hip. Therefore, the preservation of the neck should retain the trabecular system of the metaphyseal cancellous bone and allow for a physiological load within the trabecles along the diaphysis and greater trochanter. The CFP (Collum Femoris Preserving) short-stem prosthesis was introduced as a possible cementless implant for younger patients and patients with adequate bone stock.1,2 The possibility of a less invasive implantation by preserving the femoral neck has shown very valuable results in our own institution within the last ten years.3 Although there is a relatively low number of long and mid-term results for this prosthesis type, which was introduced in the mid-nineties, we were able to follow-up some of our own patients for ten-year results by now. These revealed excellent clinical and radiographic follow-ups of a total number of 155 patients.3 However, the overall number of implantations in our clinic so far has exceeded 6000 until today. In the following chapter we will give a distinct overview of the implantation technique of the CFP prosthesis in the regular as well as minimal invasive techniques. Furthermore, we will give a short overview of the existing studies as well as some technical considerations and tricks we were able to incorporate within the last ten years of successful use.
Indications and Contraindications
In general the indications for the CFP prosthesis (LINK, Hamburg Germany) in combination with the non-cemented cup system are defined by the general bone stock quality and anatomical shape and CCD-angle of the affected hip joint. In primary total hip replacement the CFP prosthesis finds its optimal setting, due to the anatomical shape along the trabecular femoral neck, in patients with a consequent normal to rather decreased CCD-angle (Fig. 22.1).4 Although increased CCD-angles above 140° can still be treated with a CFP prosthesis, in patients with a relatively vertical CCD-angle a straight stem might reconstruct the anatomical shape in a more physiological behaviour.
As the metaphyseal cancellous bone needs to be adequate to allow for a physiological load and distribution along the diaphysis and greater trochanter, patients with severe osteoporosis might not be optimal candidates for the CFP prosthesis, as they are in general not optimal candidates for noncemented hip replacements. As the intraoperative goal of the CFP stem is to provide sufficient rotational stability, the cancellous bone stock quality is of
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Figure 22.1: The collum femoris preserving stem with proximal HX coating
Figure 22.2: Metaphyseal fixation of the CFP
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Figure 22.3: The TOP (trabecular oriented pattern) cup system
high importance for the overall success rate.5,6 An optimal treatment with a CFP prosthesis is granted in patients with a physiologically high offset (Fig. 22.2). This can be adequately reproduced with the CFP prosthesis, according to the two available curvatures which will be explained in detail in the next section. In our experience we have been using the TOP (trabecular oriented pattern) (Fig. 22.3) acetabular cup (LINK, Hamburg, Germany) with the CFP prosthesis. In some rare cases where an inadequate primary stabilization of the cup could be achieved, a reversed hybrid combination of the CFP stem with a cemented all-poly cup (Mark 3, Endo Model, LINK, Hamburg) was done in our clinic.
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The Collum Femoris Preserving (CFP) Prosthesis in Primary Total Hip Replacement
Figure 22.4: Preoperative AP radiographs
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Figure 22.5: Preoperative digital templating
Preoperative Assessment and Planning
According to internal standards, preoperatively a conventional AP pelvis X-rays in combination with an axial view is done to rule out any abnormal femoral anteversion or post-traumatic limitations (Fig. 22.4). Obviously, a status postintertrochanteric fractures or valgisation osteotomies might limit the indication for the CFP. Additionally, in all cases a distinct preoperative planning based on a digital templating for the cup, the femoral head resection as well as the curvature and CCD-angle of the stem are provided (Fig. 22.5). This templating helps to differentiate between a curvature A and B prosthesis-type as well as the necessary CCD angle of 126° versus 117°, dependent on the neck-length discrepancy. The sub-capital resection is planned which usually should be performed at the isthmus. Accordingly, a distinct
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neck-length variation can still be adopted. While in our experience the 126° curvature A stem is implanted in most of our patients, some authors might prefer different implant choices on a regular basis.3
Choice of Implant
Generally, the CFP stem in combination with a TOP acetabular cup should be used according to our own experience. Thus a primary polyethylene—ceramic bearing solution is intended in all of our cases. For the ceramic head sizes we encourage 32 mm solutions and larger, depending on the patient’s activity and primary diagnosis. Age depending we recommend the Biolox forte or Biolox delta ceramic version (Ceramtec, Germany) for the bearing solution. The stem consists of titanium (Tilastan) and a calcium phosphate coating (HX) and is available in two curvature variations, either slightly (“A”) or strongly (“B”) curved. This also includes a variation of the CCD-angle in both available curvatures between 126° and 117°. According to the length and width of the stems there are actually five sizes available. These include an extra-small to an extra-large stem option. Due to the anatomical ante-curvature of the shaft, a left and right stem type is obviously available with an included anteversion of 14° (Fig. 22.6).
Operative Technique
Based on our internal clinical experience we use the posterior approach to the hip joint for all primary and revision indications. As a consequence, we also perform the posterior approach for all CFP implantations, always in the lateral position. Therefore, the following descriptions may vary somewhat depending on whether the patient is in either the supine or lateral position and the surgical approach of choice.
CUP
After the approach to the hip joint, the femoral head should be dislocated. Following dislocation, the femoral neck and the proximal rim of the trochanter should be exposed and any osteophytes on the femur removed. The optimal height for resection is the isthmus between the femoral head and neck. However, this should be compared with preoperative planning for the desired postoperative leg-length of the specific patient. The base of the major trochanter is usually 1.5 cm from the resection level. This is, however, only a rough intraoperative orientation for most cases.
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After resection of the femoral head, the acetabulum is exposed and reamed (Figs 22.7 and 22.8). Retractors are inserted, depending on whether a regular or minimal invasive operative technique is used. The reamer size should correspond to the width of the acetabular entrance. Reamers of increasing diameters are applied until areas of obvious bloody subchondral cancellous bone becomes visible. However, the surgeon should make sure that the supportive structures for secure anchoring of the metal casing are not compromised. The orientation of the reamer should correspond to the planned anteversion and inclination of the cup. The acetabulum is measured to determine the size of the cup as the reamed
Figure 22.6: The shaft includes an anteversion of 14°
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The Collum Femoris Preserving (CFP) Prosthesis in Primary Total Hip Replacement
Figure 22.7: Exposition of the acetabulum includes two Steinmann pins
Figure 22.8: Fit to size reaming
cavity may be larger than originally intended. If the patient’s bone stock is of poor quality, the surgeon might choose a cup diameter that is a few millimetres larger to ensure secure anchorage of the cup. The TOP cup can then be finally implanted using an impactor handle. The rim of the cup should be parallel to the acetabular entrance for this final secure positioning in the surrounding bone. The available alignment rod is at an angle of 90° to the body axis in each case (Fig. 22.9). The attached alignment rods give further orientation. After impaction, the central hole is closed with a locking screw (Fig. 22.10). If additional bone screws are necessary the locking screws have to be removed. This however, in our experience this is necessary in less than 0.5% of cases. The polyethylene cup is then inserted according to the existing psoas groove. A final check should be made to ensure that the polyethylene cup is adequately fixed within the titanium shell (Fig. 22.11).
FEMUR
The proximal femur is first prepared using a trocar awl to form a small hole in the resected femoral neck (Fig. 22.12). This should be continued as far as is necessary to determine the
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Figure 22.9: Alignment rods visualize the desired anteversion and inclination of the cup
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Figure 22.10: Insertion of the locking screw
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Figure 22.11: Fixation of the polyethylene inlay
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The Collum Femoris Preserving (CFP) Prosthesis in Primary Total Hip Replacement
Figure 22.12: A trocar awl identifies the canal
Figure 22.13: A curved bone curette opens the femoral canal
axis. The canal is then finally opened using a curved bone curette (Fig. 22.13). Then the stem size is determined using curved probes of increasing sizes which are inserted into the canal (Fig. 22.14). Each curved probe is inserted up to the ring mark (Fig. 22.15). The shaft up to the ring mark corresponds to the length of the bone compressor and the finally implanted stem. Preparation of the femoral canal is completed using compressors in increasing sizes to ensure adequate compression of the cancellous bone (Fig. 22.16). The choice of bone compressor depends on the stem curvature which is determined during initial planning and size assessment (Fig. 22.17). It is important to ensure that the medial teeth of the compressor do not remove the cortical bone at the calcar bow (Figs 22.18A and B). In cases where a X-small CFP prosthesis is used during the preparation of the femoral canal, no further smaller compressors are necessary. In this case, preparation of the femoral bone with the curved bone curette and a curved probe “olive” can be sufficient. The compressor is driven below the resection level to achieve a circular plane surface for the seating of the neck plate (Figs 22.19 and 22.20). Further reaming is performed with a calcar reamer (Figs 22.21 and 22.22).
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Figure 22.14: Curved probes determine the stem size
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Figure 22.15: Insertion of the probe until the ring mark
Figure 22.16: Finally compressors are used in increasing sizes
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The Collum Femoris Preserving (CFP) Prosthesis in Primary Total Hip Replacement
Figure 22.17: Sizing depends on the preoperative planning and initial curved probes
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Figures 22.18A and B: The medial teeth of the stem should not remove cortical calcar bow
Figure 22.19: The compressor is driven below the resection level
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Figure 22.20: Insertion below the resection level
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Figure 22.21: Insertion below the resection level: Close up view
Figure 22.22: Calcar reaming
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Figure 22.23: An adequate compression of the cancellous bone should be visible after compressor removal
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Figure 22.24: Figure of the remaining cancellous bone
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The Collum Femoris Preserving (CFP) Prosthesis in Primary Total Hip Replacement
Figure 22.25: Impaction of the original CFP stem with desired CCD and curvature
After final measurement of the preoperatively determined digital templating in relation to the trochanter minor, we then perform trial reduction with trial plastic heads. After final determination of the overall stability, luxation tendency and offset determined in millimetres, final luxation can be performed. Following the trial reduction and removal of the compressor, an adequate compression of the cancellous bone should become visible (Figs 22.23 and 22.24).
The final implant, (we always use HX-coated implants for our patients,7,8 is implanted
into the femur (Fig. 22.25). Due to the anatomical anteversion of the femoral neck and the CFP stem, slight impact may be applied at the lateral collar of the stem (Fig. 22.26). After final positioning the fixation screw in the neck plate must be firmly tightened in the anti-clockwise direction (Fig. 22.27). The final prosthesis head (Ceramic in our set up) is mounted onto the carefully cleaned taper of the stem and fixed with a light blow on the head using an impactor (Fig. 22.28). Following reduction a final luxation tests should again be carried out and the range of motion evaluated. A careful check should be made to detect any remaining
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Figure 22.26: A slight impaction becomes necessary
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Figure 22.27: Fixation of the neck plate screw anti-clockwise
Figure 22.28: We recommend using ceramic heads of 32 mm, if possible
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The Collum Femoris Preserving (CFP) Prosthesis in Primary Total Hip Replacement
Figure 22.29: Pelvic radiographs are recommended directly postoperative
bleeding. We recommend insertion of a deep drain into the joint. Then final closure with secure fixation of the fascia can be performed. In some cases, especially in elderly female patients, we recommend secondary suturing of the posterior capsule with nonresorbable sutures.
In general, we recommend that pelvic AP X-rays should be taken in the postoperative recovery unit immediately after surgery (Fig. 22.29). Nowadays, we recommend partial weight-bearing instead of full weight-bearing for our patients after implantation of a CFP prosthesis.
Postoperative Management
General pain management should be performed according to the hospital’s own specific treatment regime. We generally recommend leaving the drains in place for 48 hours and primary wound inspection and a dressing change during removal of the drains. Secondly, we recommend wound control every day after the drains have been removed and that sutures or staples should not be removed before the 14th postoperative day. Thrombosis prophylaxis is nowadays recommended either with low-molecular weight heparin or Dabigatran (Böhringer Ingelheim, Germany) as a new general treatment of choice for all our primary total hip and knee replacements. This should be continued until rehabilitation has been completed. We recommend that radiographs should be taken in the postoperative recovery unit immediately after surgery as well as before discharge of the patient, usually after 8 days in our clinic.
We generally encourage patients to start range of motion exercises and physiotherapy at day 1 or 2 after surgery. Partial weight-bearing is intended on day 2 and patients encouraged to walk with crutches or, in some rare cases, with a walking frame under the supervision of a physiotherapist. In cases where local bone augmentation is necessary at the acetabular TOP system, we recommend partial weight-bearing for a minimum time of 4 weeks, depended on the specific weight and compliance of the patient. In the majority of cases the crutches can be discontinued 3 to 4 weeks postoperatively. Finally, patients are able to adjust their activities as tolerated after their rehabilitation program has ended. In general we recommend
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light sporting activities such as walking, swimming, light tennis or even light skiing if the patient was performing these activities before total hip replacement.
Complications
The general complication rate for the CFP type total hip replacement does not exceed any other known hip replacement strategies or implant types. In our set-up we have so far had an overall complication rate, including disturbed wound-healing, infections, nerve injuries and technical complications, of less than 1%.7,8 To reduce the number of posterior approach-related dislocations, we recommend capsular repair during surgery. This has been shown to reduce the overall number of postoperative dislocations, especially in elderly female patients.
Internal Study Results
Our first follow-up study of the radiographic and clinical outcomes of 155 patients treated with a CFP implant revealed the following results: After an average follow-up period of 75 months the patients were evaluated according to the Harris hip score which showed a significant improvement, as expected, in 96%. The results of these 96% were either excellent or good. Only one stem had to be revised due to aseptic loosening. Thus, the overall survival rate of the CFP was 99% for the stem and 100% for the cup. Furthermore, radiological analysis showed typical patterns of remodelling with the appearance of cortical thickening, predominantly in the distal part of the prosthesis. In a few cases we found radiographic signs of osteopenia around the trochanter major region after the maximum follow-up period. The results of the study also revealed a general complication rate of less than 1%.3 Consequently, our results after a mid-term follow-up are promising and comparable to other short-stem prostheses.9-13
Conclusion
The CFP prosthesis in combination with a TOP acetabular cup system allows adequate treatment of primary total hip arthritis. Due to the anatomical shape of the prosthesis and ease of technical implantation we have been able to implant more than 6,000 prostheses in the last 10 years using either the regular or minimally invasive technique, with a high satisfaction rate in the patient and surgeon collective. The ease of implantation, impacting of the anatomically shaped stem, high reproducibility and low complication rate has technically, convinced a large number of surgeons in our clinic over the last decade. As shown in our own and other studies, the mid-term results after ten years are promising and comparable to other short-stem systems. In general, there are very few anatomical conditions which cannot be adequately treated with the CFP stem in primary total hip replacement.
Illustrative Case
A 72-year-old woman underwent primary total hip replacement in 1999 on her right side based on a progressive osteoarthritis and severe clinical symptoms (Figs 22.30A and B). Consecutive two years after her right hip, she also underwent successful replacement of the left hip with the CFP prosthesis (Fig. 22.30C). At 12 and 10 years after the right and the left replacement respectively, the patient showed excellent clinical results and radiographs showed no sign of loosening, no poly-wear with adequate prosthetic fixation on both hips (Figs 22.30D and E). The adequate preservation of the femoral neck becomes visible bilaterally including the complete osteointegration of both stems and cups.
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Figure 22.30A: Progressive OA of the right hip in 1999 before primary CFP implantation
Figure 22.30B: Two years after right side implantation, with now increasing clinical symptoms of the left hip in 2001
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The Collum Femoris Preserving (CFP) Prosthesis in Primary Total Hip Replacement
Figure 22.30C: Radiograph at discharge after left side treatment in 2001
Figure 22.30D: Current anteroposterior radiographs at longest follow up, 12 years after implantation on the right side, 10 years at left side, respectively
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Figure 22.30E: Current lateral radiographs bilateral at latest follow-up
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Decking R, Reuter P, Huttner M, Puhl W, Claes LE, Scharf HP. Surface composition analysis of failed cementless cocr- and ti-base-alloy total hip implants. J Biomed Mater Res B Appl Biomater 2003;64:99-106.
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Jakubowitz E, Seeger JB, Lee C, Heisel C, Kretzer JP, Thomsen MN. Do short-stemmed-prostheses induce periprosthetic fractures earlier than standard hip stems? A biomechanical ex-vivo study of two different stem designs. Arch Orthop Trauma Surg 2009;129:849-55.
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Rohrl SM, Li MG, Pedersen E, Ullmark G, Nivbrant B. Migration pattern of a short femoral neck preserving stem. Clin Orthop Relat Res 2006;448:73-8.
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Stea S, Bordini B, De Clerico M, Petropulacos K, Toni A. First hip arthroplasty register in Italy: 55,000 cases and 7 year follow-up. Int Orthop 2009;33:339-46.