Femoral Diaphyseal Cortical Hypertrophy Following Revision Hip Arthroplasty using an AcuMatch® M-Series Stem

D. Gordon Allan, MD, FRCS(C)
Chairman of Orthopaedics; Southern Illinois University
School of Medicine, Springfield, IL

Presentation

A 52-year-old male physician underwent a left cemented bipolar hip arthroplasty in 1995 for avascular necrosis secondary to corticosteroid medication after renal transplantation. Six years later, he presented with complaints of increasing groin and thigh pain as well as shortening of the leg. X-rays showed extensive osteolysis of the femur and in the medial and posterior aspects of the acetabulum. There was approximately 4 centimeters of femoral subsidence (Figure 1). The patient elected to undergo revision hip arthroplasty.

Surgical Details

The patient was positioned laterally and prepped and draped in the usual fashion. The original posterolateral scar was reopened and extended distally. The underlying hip joint was encountered after dissection through the soft tissues and was dislocated posteriorly. The existing femoral component was extracted almost without any effort, as it was grossly loose. The cement mantle was removed in a piecemeal manner along with a very thick membrane. An intra-operative Gram stain and frozen section were negative for acute inflammation.

The acetabulum was reamed and the large defect in the medial wall of the acetabulum was filled with a 45mm disk of Opteform® bone graft material. An HA-coated acetabular component was impacted into place and secured with two screws. A posteriorly elevated acetabular polyethylene liner was impacted into the cup.

A cerclage wire was placed around the proximal femur prophylactically. Cylindrical reaming was performed up to 17mm to a depth corresponding to 200mm. Medially, the bone was deficient to a level just below the lesser trochanter. To prepare for the metaphyseal portion of the AcuMatch® M-Series stem, conical reaming was done up to size 29. Milling of the metaphyseal flare was then completed out to a size 29 large. Trial reductions were done with a 17x200mm diaphyseal stem, a 29 large metaphyseal component and standard high offset proximal neck segment. AP and lateral intra-operative Xrays were obtained and once we were satisfied with these, the definitive stem and metaphyseal components were impacted into place. Trial reductions were performed with a variety of neck segments. A standard high offset neck segment was chosen along with a 28mm head with a +5mm head length in order to best restore the patient’s hip stability and offset. These definitive components were impacted in the desired anteversion and the locking bolt secured. No femoral bone grafting was done. The hip was reduced and found to be stable both anteriorly and posteriorly. Final AP and lateral intra-operative X-rays were obtained to confirm that no cortical penetration or fracture had occurred with the insertion of the implants. Final films looked fine and the operative site was closed in a standard fashion.

Results

Post-operatively he did well and was discharged on the third day, restricted to featherweight bearing for six weeks. At the six-week visit, the patient was advanced to weight bearing as tolerated and conditioning exercises were initiated. By the three-month visit, he was walking without aids and had resumed his normal activities including Tai Chi.

The patient has been followed yearly with a four-year follow-up. Early post-op X-rays (three month) show a stable construct with evidence of the preoperative osteolysis (Figure 2). The length and offset have been restored and the patient is functioning well. Post-operative films at four years show a remarkable amount of regeneration of the metaphyseal and diaphyseal regions of the patient’s proximal femur (Figure 3). Due to metaphyseal fixation, physiologic loads have been distributed through the femoral diaphysis resulting in cortical hypertrophy.

Figure 1: Pre-op – Note the osteolysis, cortical thinning and femoral subsidence.		Figure 2: Three-month post-op.		Figure 3: Four-year post-op.

Discussion

The AcuMatch M-Series femoral stem is a good implant choice for revision arthroplasty in patients who present with poor bone quality. Its interchangeability allows for intra-operative flexibility to ensure a stable joint and the proximal loading of the metaphyseal component imparts the stresses required to prevent further bone resorption and even encourage bony remodeling. Bone preparation with this system is rather atraumatic and is of particular value in revision cases in which the bone is thin and friable. Bone preparation through reaming and milling is less apt to produce an iatrogenic femoral fracture as compared to broach preparation.

The ability to uncouple diaphyseal and neck orientation is of value in revision cases as the diaphysis is often remodeled in varus. When a long curved stem is used, the canal tends to accept the stem bow with the apex laterally. With a one-piece stem, the canal may need to be overreamed and the surgeon must strive to keep the stem in the desired final anteversion during insertion. This can result in a stem that is inserted in excessive anteversion or a femoral fracture as the stem is de-rotated. With a three-piece modular stem, the diaphyseal component is inserted to conform to the existing bone and the neck orientation is selected afterwards.

Likewise, when a cemented femoral stem loosens, the metaphysis typically is remodeled in retroversion. A one-piece stem that fills the metaphysis would therefore be retroverted. Conversely, a two-piece modular cylindrical stem could be used, but limited loading of the metaphyseal bone will result. With a modular three-piece stem, the metaphysis and the diaphysis can be fit independently to minimize the amount of recontouring of the bone necessary, either by substantial reaming or femoral osteotomy.

This stem also features sharp diaphyseal flutes for initial rotational control, important in early implant stability or to bridge femoral fractures or osteotomies. The coronal slot decreases the stiffness of the stem and reduces the likelihood of cortical penetration during insertion.

The AcuMatch M-Series modular femoral stem simplifies technically challenging femoral revisions with features such as ream and mill bone preparation, comprehensive trialing and low-profile implant insertion. Additionally, the broad scope of distal stem, metaphyseal and neck implants, enables the creation of a prosthesis customized to the unpredictable femoral anatomy typical of revision THA. The proximal loading of the AcuMatch M-Series design promotes cortical hypertrophy and regenerates lost bone without grafting.

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