RECONSTRUCTION 2023, Jan, 26 | 12:00 am

Modular Stems

 

Modular Stems

 

 

INDICATIONS

While useful in most hips requiring primary total hip arthroplasty (THA), modular femoral stems are especially indicated in conditions with abnormal acetabular and/or femoral anatomy (1). Elements of developmental dysplasia of the hip (DDH) and deformity occur frequently in primary THA (2,3,4,5,6,7). A review of 75 hips with a diagnosis of idiopathic osteoarthritis revealed proximal femoral deformity in 40% of hips and acetabular dysplasia in 39% of hips (5). The variable shape of the femoral canal (canal/flare index; proximal/distal mismatch) may cause difficulty in achieving proximal and distal fit and fill with standard femoral components (8).

Other frequent conditions producing distorted anatomy include prior surgery (e.g., osteotomy), posttraumatic deformity, secondary osteoarthritis (e.g., Legg-Calve-Perthes disease, slipped capital femoral epiphysis, and sepsis), as well as coxa vara and coxa valga deformities. Less common conditions include small femoral canals (e.g., juvenile rheumatoid arthritis, dwarfism, spondylope-ripheral dysplasia), large femoral canals (Dorr Type C bone (9), ankylosing spondylitis, rheumatoid arthritis, and alcoholic bone disease), and Paget disease.

Modular femoral components offer a large array of femoral offset, length, and version options (10), which can be used independently or in combination to recreate normal biomechanics and a well-tensioned soft tissue envelope (11).

 

CONTRAINDICATIONS

Contraindications to the modular femoral stems are rare but might include extreme femoral canal deformity where cemented or custom stem fixation is more easily achieved. The direct anterior approach is contraindicated when using a modular femoral stem.

 

 

PREOPERATIVE PLANNING

Detailed history, physical, and radiographic evaluation are required for any patient undergoing primary THA. The history should focus on prior treatments, surgeries, and complications. The patients' disabilities (leg length, fatigue, limp, etc.) and pain pattern should be thoroughly discussed.

Physical examination will often reveal abnormalities in size, range of motion (stiffness or laxity), leg lengths, and prior incisions, which can make surgery more difficult. Surgeries to the contralateral limb (e.g., epiphysiodesis) should be noted. Leg lengths are assessed by tape measure and blocks under the short limb to determine exact discrepancies and what length appears to best balance the pelvis. Thorough preoperative assessment of femoral and sciatic nerve function is essential.

Plain radiographs should include an anteroposterior (AP) projection pelvis and AP and Lauenstein lateral x-rays of the involved hip. Radiographic magnification markers taped to the involved hip allow for an accurate estimate of x-ray magnification, permitting precise femoral canal sizing and templating. Computer tomography (CT) scans

 

are rarely indicated but can provide more accurate assessment of anteversion, femoral canal dimensions, and acetabular bone stock assessment. Scanograms may be useful to more accurately assess limb length inequalities.

 

TECHNIQUE

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The patient is positioned in the lateral decubitus position with the affected side up. The underlying leg is paced in flexion to reduce the degree of lumbar lordosis. The trunk and pelvis are appropriately stabilized while the operated leg is prepped. We drape the operated leg free over a radiolucent table to permit possible fluoroscopic evaluation.

Anterolateral, direct lateral, and posterior approaches may be used with modular stems. I prefer the posterior approach to avoid scars from prior anterior surgeries (common in DDH), minimize damage to the abductors, and easily identify, protect, and monitor the sciatic nerve. The posterior approach can be easily converted to a trochanteric or subtrochanteric osteotomy for a stiff hip, distorted anatomy, or high-riding DDH cases (see Fig. 18-1).

For thin, flexible hips requiring less than 1-cm limb lengthening, a small incision is made from the midpoint of the vastus tubercle extending proximally and posteriorly for 4 to 6 inches (see Fig. 18-2). The incision is extended further proximally and distally for larger and stiff patients, especially those requiring trochanteric or subtrochanteric osteotomy or limb lengthening greater than

 

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1 cm. The fascia lata and gluteus maximus are divided in line with the incision. The sciatic nerve is identified by palpation but not dissected. Partial or full release of the gluteus maximus tendon at the linea aspera may be performed to prevent tethering of the sciatic nerve during manipulation of stiff hips or lengthening of greater than 1 cm. The piriformis tendon is released from its fossa to expose the inferior capsular recess. Other external rotators are released as needed and reflected posteriorly to further protect the sciatic nerve, which may be scarred or displaced in cases with distorted anatomy. Cobra retractors are then placed superiorly under the gluteus minimus muscle and in the inferior capsular recess. While posterior capsulotomy and repair are performed in most cases, including Crowe I and II DDH hips (see Fig. 18-3), capsulectomy may need to be performed in selected stiff hips, especially those requiring further exposure or significant limb lengthening (e.g., Crowe III and IV DDH hips). A smooth 7/16-inch Steinman pin can be placed into ischium at the level of the transverse ligament for limb length assessment prior to dislocation and after trial reduction.

 

 

 

FIGURE 18-1 Preoperative (A) and postoperative (B) AP pelvis x-ray demonstrating transtrochanteric approach required for marked stiffness from prior bilateral iliac osteotomies.

 

 

 

 

 

FIGURE 18-2 The standard incision is lateral, from the midpoint of the vastus tubercle extending proximally and posteriorly for 4 to 6 inches. It can be easily extended proximally and distally for more extensile exposure (see dotted lines).

 

The hip is dislocated posteriorly if not already severely subluxed or dislocated (Crowe III and IV hips) (3). The greater and lesser trochanters and femoral head are used as landmarks in conjunction with preoperative templates to determine the level of femoral neck osteotomy (see Fig. 18-4). When subtrochanteric osteotomy

(12) is performed to help reduce high-riding Crowe III and IV hips, the femoral canal is prepared distally and proximally and a trial sleeve is positioned in the proximal

 

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femur (see Fig. 18-5). The vastus lateralis is then reflected from the vastus tubercle distally for 6 to 10 cm. The linear aspera is identified, and rotation marks are made on the femur prior to the osteotomy. The iliopsoas tendon is sectioned just proximal to its insertion at the lesser trochanter. The transverse osteotomy is then made distal to the sleeve and approximately 3.5 cm distal to the lesser trochanter (see Fig. 18-6). The acetabulum is then easily exposed by complete capsulectomy

 

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and anterior displacement of the proximal femoral fragment and attached abductors (see Fig. 18-7). If

subtrochanteric osteotomy is not performed, then the capsule is dissected inferiorly until the transverse ligament and true socket are identified. The acetabulum is then prepared and positioned. Acetabular bone deficiencies may require cup placement more medial, superior, or in more abnormal version than desired in cases with distorted anatomy. The advantage of the modular stem in this setting is that it can easily accommodate to these abnormal socket positions by increasing offset, neck length, or independent version of the stem from the sleeve to maximize myofascial tension, leg length, and stability, while avoiding implant impingement.

 

 

 

FIGURE 18-3 Preoperative (A) and postoperative (B) AP pelvis x-ray in patient with Crowe I and Crowe II dysplasia. Acetabular structural autograft is used for the Crowe II hip. Note difference in proximal sleeve placement to accommodate for version differences.

 

 

 

 

 

FIGURE 18-4 A femoral neck resection template for stem size, neck length, and offset determines the level of initial femoral neck osteotomy.

 

 

 

 

 

FIGURE 18-5 Preparation of the femoral canal is performed prior to subtrochanteric osteotomy.

 

 

 

FIGURE 18-6 Initial transverse osteotomy distal to the trial sleeve, approximately 3.5 cm distal to the lesser trochanter.

 

Each modular stem has its unique nuances. I use the S-ROM stem (DePuy, Warsaw, IN). The following technique applies to this stem. The femoral canal is identified with a box osteotome and canal finder. A three-step milling process then prepares the femoral canal. Step one involves cylindrical diaphyseal reaming until firm endosteal cortical contact is achieved to prepare the distal femur

 

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(see Fig. 18-8). In small femoral canals or Type A bone, begin with the smallest diameter reamer and increase in 0.5- to 1.0-mm increments. The final reamer should match or be 0.5 mm greater than the minor diameter of the chosen stem. If subtrochanteric osteotomy has been performed, reamers can be placed into the distal bone fragment through the osteotomy site to a depth matching or exceeding the final stem placement after excision of the subtrochanteric fragment.

 

 

 

FIGURE 18-7 Acetabular exposure is excellent after completion of the osteotomy.

 

The proximal femur is prepared in two steps. A shaft pilot, matching the minor stem diameter, directs proper placement of the proximal reamers. Conical metaphyseal reamers in 2-mm increments are placed until firm AP proximal diaphyseal and metaphyseal contact is obtained without excessive thinning of the proximal endosteal cortex (see Fig. 18-9). Calcar miller reamers are then used to mill

 

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the metaphyseal flare to maximize host bone contact irrespective of sleeve version (see Fig. 18-10). Femoral sleeve and stem trials are then placed. There are ten sleeve options for each diameter stem. The trial neck can be rotated in 10 degree increments until desired stem anteversion is achieved (see Fig. 18-11). Femoral neck and head options are then selected to provide desired leg length and offset.

 

 

 

FIGURE 18-8 Cylindrical diaphyseal reamers in 0.5-cm increments prepare the diaphysis until firm cortical contact is achieved. Etching on the reamer references greater trochanter and anticipated hip center.

 

 

 

 

 

FIGURE 18-9 Conical reamers in 2-mm increments prepare the metaphyseal bone until firm anterior/posterior contact is achieved. The distal pilot corresponds in size to the last cylindrical diaphyseal reamer utilized.

Etchings on reamer reference neck length and hip center relative to greater trochanter.

 

 

 

FIGURE 18-10 The triangle calcar miller prepares the metaphyseal flare in the version that allows maximum contact with host bone. The distal pilot and proximal cone pilot correspond to the final distal and proximal reamers previously used. Etchings on reamer reference neck length and sleeve size.

 

 

 

 

 

FIGURE 18-11 The trial neck assembly can be rotated in 10-degree increments until desired stem anteversion is achieved, independent of sleeve placement.

 

 

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Trial reduction is then performed to assess leg length, stability, combined anteversion, and range of motion. If limb lengthening has been performed, begin the initial reduction with the shortest neck length and offset trial and slowly increase both as desired. Soft tissue releases of the capsule, gluteus maximus tendon, iliotibial band,

tensor fascia lata, straight head of the rectus femoris tendon, and iliopsoas tendon are performed until desired tissue tension and leg length are achieved in difficult cases. When subtrochanteric osteotomy has been performed, the trial stem and sleeve are placed into the proximal fragment and reduced into the acetabular component. With the leg in full extension, an assistant then distracts the distal fragment, and the amount of overlap between the distal and proximal bone fragments determines the amount of initial subtrochanteric bone to be resected (see Fig. 18-12). A second transverse osteotomy is then made in the distal fragment. Trial reduction can then be completed, correcting for anteversion abnormalities either through the stem placement or derotation of the osteotomy fragment (see Fig. 18-13). A Lowman bone clamp stabilizes the fragment during trial reduction and implant insertion.

 

 

 

 

FIGURE 18-12 With the trial reduced, distraction of the distal fragment will estimate the amount of distal bone to be resected by measuring overlap between the two fragments.

 

 

 

 

 

FIGURE 18-13 Preoperative (A) and 9-year postoperative (B) x-rays after bilateral subtrochanteric osteotomies for high-riding DDH.

 

 

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Upon trial implant removal, differences in stem and sleeve anteversion are noted. The real sleeve is then

inserted into the prepared proximal femur, and the stem is introduced in the proper amount of anteversion (see Fig. 18-14). Final reduction is then performed with a desired combined anteversion of 40 to 45 degrees for posterior approaches and 35 to 40 degrees for hips dislocated anteriorly. If subtrochanteric osteotomy is performed, rotational stability is assessed. Either a unicortical plate or a cortical onlay allograft is applied if the osteotomy is not completely stable rotationally.

 

 

 

FIGURE 18-14 Orientation lines in 20-degree increments on the implanted sleeve are matched to the stem/neck witness mark to assure proper version of the stem/neck during implantation.

 

PEARLS AND PITFALLS

 

Use of femoral component modularity requires surgeon and operative team familiarity with the options and inventory required of the 3-step milling process to avoid complications.

 

Fractures are less common with milling versus broaching of the femoral envelope (13,14). Most intraoperative fractures occur during trochanteric impingement with distal diaphyseal reamers or over aggressive conical and/or calcar milling of the proximal femur.

 

Trochanteric fractures can be avoided by either trochanteric osteotomy or trimming of the posterior/proximal trochanter to avoid impingement during diaphyseal reaming.

 

Proximal neck fractures can be minimized by careful milling or burring (e.g., sclerotic posttraumatic bone) of the proximal femur. Oversizing of the proximal sleeve should be avoided by sequential sizing of the trial sleeve implant. When inserting the real implant, leaving the sleeve slightly proximal assures locking of the stem/sleeve taper before the combined unit is impacted to the level of the milled femur. Sequential femoral component impaction should stop when the neck cut level established during trial implantation is achieved.

 

Trochanteric abutment against the ischium in extension, especially in hips with a high hip center, can be minimized by derotational subtrochanteric osteotomy or trimming of the posterior trochanter and/or lateral ischium.

 

A subtrochanteric osteotomy is preferred to a trochanteric advancement with femoral neck shortening in order to avoid problems with trochanteric fixation (nonunion, fibrous union, bursitis).

 

POSTOPERATIVE MANAGEMENT

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The patient is transferred by stretcher or standard orthopedic bed with a regular pillow between the legs. An AP pelvis and operative hip x-ray are obtained in the PACU to access proper implant positioning and to exclude dislocation and/or fracture. Drains are not routinely used. Ambulation begins either the day of surgery (accelerated rehab) or postoperative day one. Crutches with weight bearing as tolerated are used until seen at 3 to 4 weeks post-op. Protective weight bearing and prolonged crutch use (6 to 8 weeks) are used in cases of subtrochanteric osteotomy or trochanteric osteotomy. Hip abductor precautions are also used for 8 weeks in these select patients.

 

 

COMPLICATIONS

Excessive limb lengthening and nerve palsy are serious complications of primary THA when using modular stems in patients with femoral deformity and DDH. Accurate preoperative and intraoperative leg length assessment is critical. It is useful to place a leg length pin in the ischium near the desired hip center before dislocation. The pin's axial position can be marked on the vastus lateralis with a stitch before dislocation and after reconstruction. Limb lengthening greater than 2.5 cm should be avoided in order to minimize risks of femoral and sciatic nerve palsy. During surgery, limited hip flexion (20 to 30 degrees) and knee flexion (30 to 40 degrees) minimize excess tension on the femoral and sciatic nerves. Femoral and sciatic nerve palsies occur most frequently in patients who have had prior surgery in which anterior or posterior scars inhibit nerve excursion during limb lengthening. Careful and gentle retractor placement must be constantly monitored. Finally, in patients undergoing limb lengthening greater than 2.0 cm, an awake test is performed to assess sciatic and femoral nerve function. Preoperative patient instruction and anesthesia cooperation are required. Sciatic nerve evoked potential monitoring during surgery may also be useful.

Other potential complications of modular stems include femoral fractures and trochanteric complications. For small femoral canals, power milling is preferable to broaching, and smaller-than-standard instruments and implants may be needed. For short femurs or femurs shortened by subtrochanteric excisional osteotomy, perforation of the anterior femoral bow can be avoided by flexible reaming of the canal or shortening the femoral implant with a metal cutting device.

 

RESULTS

Excellent results of the S-ROM (DePuy Orthopaedics, Inc., Warsaw, IN) modular femoral component have been well documented for use in primary THA. Cameron et al. (15) reported 2- to 5-year results on 81 hips, 14% having undergone prior surgery. Three hips were revised for socket migration and one for late dislocation. Two percent of the patients had mild thigh pain, and there were no cases of femoral loosening. In a further follow-up study (16) of 380 primary S-ROM stems at 5 to 17 years (mean 9.4 years), only 2 patients had osteolysis distal to the stem/sleeve junction. All stems achieved ingrowth, with one stem failing from periprosthetic fracture requiring revision. Christie et al. (17) reported on a multicenter, retrospective review of 175 S-ROM stems at 4 to 7.8 years (mean 5.3 years). One femoral component was revised for aseptic loosening and 98% were radiologically ingrown. Osteolysis occurred in 12 patients (7%) but was present only above the sleeve, comparable to other contemporary series of THA in the literature. No complications related to the modular junctions were identified. Tanger et al. (18) reported on 59 primary S-ROM stems, with the mean follow-up of 101 months (range, 72 to 145 months). All stems showed bony ingrowth, and no stems were revised despite 48% of the stems being undersized.

 

 

Other published results demonstrate the advantages of modularity with excellent results and few complications, including these indications: optimizing femoral anteversion and stability (11,19,20), DDH (21), femoral deformity (22), leg length inequality (23), and proximal/distal mismatch (24). Multiple authors also have reported the use of the S-ROM stem in both primary and revision circumstances requiring femoral osteotomy. The advantages of milling versus broaching to reduce fracture incidence and improve prosthesis/bone contact have been well documented (13,14,25).

Extensive work by Bobyn (26,27,28,29) and others (30) has demonstrated some minor fretting and rare particle production from the stem/sleeve junction. With testing out to 20 million cycles, the levels of metallic particles were found to be several orders of magnitude smaller than the levels of the polyethylene particles generated in hips due to acetabular component wear (26). Bono et al. (31) also collected synovial samples in 19 patients with an S-ROM stem at an average of 38 months (range 6 to 89 months). No titanium debris was collected in 17 patients. The two patients with titanium debris had loose acetabular components and screws.

Clinically, osteolysis in association with the S-ROM stem has been low (15,16,17,18,26,32,33,34,35,36,37,38). A concern about modular stems is that the taper will not provide an adequate seal, causing the stem distal to the taper to become part of the effective joint space. Cameron

(16) studied 380 primary S-ROM stems at 5 to 17 years (mean 9.4), and only 2 femurs had osteolysis distal to the stem/sleeve junction.

 

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Both of these hips had aseptic loosening of the proximal sleeve. He concluded that a stem/sleeve morse taper provides an adequate seal to particular debride in well-fixed implants.

Fixation obtained by the proximal sleeve has been reliable and durable (39,40). Lee et al. (39) documented in synthetic femurs that the S-ROM sleeve could obtain rigid fixation. Ohl et al. (40) also demonstrated the excellent torsional fixation of the S-ROM modular stem, equivalent to cemented stems, in cadaver bone.

This initial stability and fixation may be useful in patients undergoing accelerated rehabilitation or when treating distal periprosthetic fractures (see Fig. 18-15).

 

 

 

FIGURE 18-15 Serial x-rays demonstrating versatility of modular stems in femoral deformity and periprosthetic fractures. A: Preoperative x-ray demonstrating proximal deformity after femoral osteotomy. B: Postoperative x-ray shows proximal sleeve triangle placed laterally to improve host bone contact. A calcar replacement neck was used to accommodate for low neck cut and to equalize leg lengths. C: Transverse fracture below stem at 2 years postoperatively after falling from 8-feet staging. D: The index stem has been replaced with a longer stem, leaving the original sleeve in place. Flexible reamers can be placed through the sleeve to prepare the distal femur. A cortical onlay graft has been added.

 

 

 

 

REFERENCES

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  1. Buly R, Christie M, Goldstein WM, et al.: The modular advantage: a comparison of stem/sleeve modularity versus one-piece stems in total hip arthroplasty. Orthopedics 23(9): 1025-1124, 2005.

     

     

  2. Anderson MJ, Harris WH: Total hip arthroplasty with insertion of the acetabular component without cement in hips with total congenital dislocation or marked congenital dysplasia. J Bone Joint Surg Am 81(3): 347-354, 1999.

     

     

  3. Crowe, JR, Mani VJ, Ranawat CS: Total hip replacement in congenital dislocation and dysplasia of the hip. J Bone Joint Surg Am 61(1): 15-23, 1979.

     

     

  4. Garvin KL, Bowen MK, Salvati EA, et al.: Long-term results of total hip arthroplasty in congenital dislocation and dysplasia of the hip. J Bone Joint Surg Am 73(9): 1348-1354, 1991.

     

     

  5. Harris WH: Etiology of osteoarthritis of the hip. Clin Orthop Relat Res 213: 20-33, 1986.

     

     

  6. MacKenzie JR, Kelley SS, Johnston RC: Total hip replacement for coxarthrosis secondary to congenital dysplasia and dislocation of the hip: long-term results. J Bone Joint Surg Am 78(1): 55-61, 1996.

     

     

  7. Sanchez-Sotelo J, Berry DJ, Trousdale RT, et al.: Surgical treatment of developmental dysplasia of the hip in adults: II. Arthroplasty option. J Am Acad Orthop Surg 10(5): 334-344, 2002.

     

     

  8. Noble PC, Alexander JW, Lindahl LJ, et al.: The anatomic basis of femoral component design. Clin Orthop Relat Res 235: 148-165, 1988.

     

     

  9. Dorr LD: Optimizing results of total joint arthroplasty. Inst Course Lect 34: 401-404, 1985.

     

     

  10. Buly R: The S-ROM stem: versatility of stem/sleeve combinations and head options. Orthopedics 23(9): 1025-1032, 2005.

     

     

  11. Dennis DA, Lynch CB: Stability advantages of a modular total hip system. Orthopedics 23(9): 1049-1052, 2005.

     

     

  12. Masonis JL, Patel JV, Miu A, et al.: Subtrochanteric shortening and derotational osteotomy in primary total hip arthroplasty for patients with severe hip dysplasia. J Arthroplasty 18(3 Suppl 1): 68-73, 2003.

     

     

  13. DeBuar DK: Advantages of milling versus broaching the proximal femur. Orthopedics 23(9): 1041-1044, 2005.

     

     

  14. Talmo CT, Bono JV: Preventing and managing intraoperative fractures and perforations in total hip arthroplasty. Orthopedics 23(9): 1085-1088, 2005.

     

     

  15. Cameron HU, Jung YB, Gruen TA: Noncemented proximally modular total hip replacement: a two to five year follow-up. Contemp Orthop 26: 1993.

     

     

  16. Cameron HU: Modular junctions. Orthopedics 23(9): 1057-1058, 2005.

     

     

  17. Christie MJ, DeBoer DK, Trick LW, et al.: Primary total hip arthroplasty with use of the modular S-ROM

    prosthesis. Four to seven year clinical and radiographic results. J Bone Joint Surg Am 81: 1707-1716, 1999.

     

     

  18. Tanzer M, Chan S, Brooks CE, et al.: Primary cementless total hip arthroplasty using a modular femoral component: a minimum 6 year follow-up. J Arthroplasty 16(8 Suppl 1): 64-70, 2001.

     

     

  19. Polili J: The S-ROM stem and its use with alternative bearings. Orthopedics 23(9): 1053-1056, 2005.

     

     

  20. Kudrua JC: Femoral version: definition, diagnosis, and intraoperative connection with modular femoral components. Orthopedics 23(9): 1045-1048, 2005.

     

     

  21. Mattingly DA: The S-ROM modular stem for femoral deformities. Orthopedics 23(9): 1059-1062, 2005.

     

     

  22. Mattingly DA: The S-ROM modular femoral stem in dysplasia of the hip. Orthopedics 23(9): 1069-1074, 2005.

     

     

  23. Goldstein WM, Gordon A, Branson JT: Leg length inequality in total hip arthroplasty. Orthopedics 23(9): 1037-1040, 2005.

     

     

  24. Christie M, Brinson MF: Proximal/distal mismatch: type A and C femurs. Orthopedics 23(9): 1033-1036, 2005.

     

     

  25. Paul HA, Bargar WL, Mittlestadt B, et al.: Development of a surgical robot for cementless total hip arthroplasty. Clin Orthop 285: 57-66, 1992.

     

     

  26. Bobyn J, Dujovne A, Krygier J, et al.: Surface analysis of the taper junctions of retrieved and in vitro tested modular hip prostheses. In: Morrey B, ed. Biological, material and mechanical considerations of joint replacement. New York, NY: Raven Press Ltd, 1993.

     

     

  27. Bobyn JD, Tanzer M, Krygier JJ, et al.: Concerns with modularity in total hip arthroplasty. Clin Orthop

    298: 27-36, 1994.

     

     

  28. Krygier JJ, Bobyn JD, Dujovne AR, et al.: Strength, stability and wear analysis of titanium femoral hip prostheses tested in fatigue. Presented at: Transactions of the 4th World Biomaterials Congress, Berlin, Germany, 1992.

     

     

  29. Krygier JJ, Dujoven AR, Bobyn JD: Fatigue behavior of titanium femoral hip prosthesis with proximal sleeve-stem modularity. J Appl Biomater 5: 195-201, 1994.

     

     

  30. Postak PD, Polando G, Pugh JW, et al.: A new method of fatigue testing for proximally supported femoral stems. Trans AAOS 320, 1990.

     

     

  31. Bono JV, McCarthy JC, Lee J, et al.: Fixation with a modular stem in revision total hip Arthroplasty. Instr Course Lect 49: 131-139, 2000.

     

     

  32. Spitzer AI: The S-ROM cementless femoral stem: history and literature review. Orthopedics 23(9): 1117-

    1124, 2005.

     

     

  33. Cameron HU, Jung YB, Noiles DG, et al.: Design features and early clinical results with a modular proximally fixed low bending stiffness uncemented total hip replacement. Scientific exhibit presented at: AAOS, Atlanta, GA, 1998.

     

     

  34. Cameron HU, Trick LW, Shepherd B, et al.: An international multi-center study on thigh pain in total hip replacements. Scientific exhibit presented at: AAOS, New Orleans, LA, 1990.

     

     

  35. Cameron HU: The 3-6 year results of a modular noncemented low-bending stiffness hip implant: a preliminary study. J Arthroplasty 8: 239-243, 1993.

     

     

  36. Cameron HU: Point-counterpoint: modularity in primary total hip arthroplasty. J Arthroplasty 11: 332-334, 1996.

     

     

  37. Cameron HU, Lee OB, Chou H: Total hip arthroplasty in patients with deficient bone stock and small femoral canals. J Arthroplasty 18: 35-40, 2033.

     

     

  38. Sporer SM, Obar RJ, Bernini PM: Primary total hip arthroplasty using a modular proximally coated prosthesis in patients older than 70: two to eight year results. J Arthroplasty 19: 197-203, 2004.

     

     

  39. Lee TQ, Danto MI, Kim WC: Initial stability comparison of modular hip implants in synthetic femurs.

    Orthopedics 21: 885-888, 1998.

     

     

  40. Ohl MD, Whiteside LA, McCarthy DS, White SE: Torsional fixation of a modular femoral hip component.

Clin Orthop 287: 135-141, 1993.