Ormonde M. Mahoney

The Effect of Femoral Component Position on Patellar Tracking After Total Knee Arthroplasty

In a laboratory study, seven fresh anatomic knee specimens were evaluated to define the three-dimensional motions of the patella before and after total knee arthroplasty (TKA) with the AMK knee. The patella was displaced medially by an average of 4 mm and tilted medially by an average of 4 degrees after standard TKA. Medial translation or internal rotation of the femoral component further displaced and tilted the patella medially, but lateral translation or external rotation of the femoral component produced less predictable changes in patellar tracking. The patterns of patellar tracking after external rotation of the femoral component came closer to reproducing those of the intact knee than any other femoral component position. The high lateral ridge on the femoral component effectively prevents patellar dislocation but may produce abnormally high stresses on the patellar implant, especially if the implant is medially displaced or internally rotated. This could lead to accelerated wear or loosening of the patellar component.

The effect of continuous epidural analgesia on postoperative pain, rehabilitation, and duration of hospitalization in total knee arthroplasty.

Efficacies of three alternate methods of postoperative analgesia were studied in 156 patients who had total knee arthroplasty (TKA). Forty-two of these patients received parenteral meperidine hydrochloride or morphine (Group 1), 58 patients received periodic epidural injections of morphine (Group 2), and 56 patients received continuous epidural infusions of bupivacaine hydrochloride and Duramorph (Group 3). The postoperative course of all patients was documented in terms of the incidence and severity of pain, range of joint motion, duration of hospitalization, and occurrence of complications. Although epidural analgesia increased the cost and duration of the operation, good-to-excellent pain relief was attained in 86% (Group 2) and 88% (Group 3) of cases with epidural analgesia compared with 61% of patients (Group 1) receiving conventional analgesia. Moreover, 67% of patients in Group 1 experienced frequent episodes of moderate-to-severe postoperative pain in contrast to 40% of patients in Group 2 and only 10% of patients in Group 3. As a result of diminished pain, greater joint motion was obtained within the first 72 hours in Groups 2 and 3. They also had shorter hospitalization (9.6 days versus 11.2 days for Group 1 and 10.8 days for Group 2). However, the use of epidural analgesia did not reduce the incidence of complications, including nausea. Continuous infusion of epidural bupivacaine and Duramorph provided good-to-excellent control of postoperative pain after TKA. However, better analgesics are needed to reduce the high incidence of side effects associated with various treatment methods.

Overhang of the Femoral Component in Total Knee Arthroplasty: Risk Factors and Clinical Consequences

BACKGROUND Recently, much attention has been directed to femoral component overhang in total knee arthroplasty. The purposes of this study were to describe the prevalence of femoral component overhang among men and women after total knee arthroplasty, to identify risk factors for overhang, and to determine whether overhang was associated with postoperative knee pain or decreased range of motion. METHODS Femoral component overhang was measured intraoperatively during 437 implantations of the same type of total knee arthroplasty prosthesis. The overhang of metal beyond the bone cut edge was measured in millimeters at the midpoint of ten zones after permanent fixation of the implant. Factors predictive of overhanging fit were identified, and the effect of overhang on postoperative pain and flexion was examined. RESULTS Overhang of >or=3 mm occurred in at least one zone among 40% (seventy-one) of 176 knees in men and 68% (177) of 261 knees in women, most frequently in lateral zones 2 (anterior-distal) and 3 (distal). Female sex, shorter height, and larger femoral component size were highly predictive of greater overhang in multivariate models. Femoral component overhang of >or=3 mm in at least one zone was associated with an almost twofold increased risk of knee pain more severe than occasional or mild at two years after surgery (odds ratio, 1.9; 95% confidence interval, 1.1 to 3.3). CONCLUSIONS In this series, overhang of the femoral component was highly prevalent, occurring more often and with greater severity in women, and the prevalence and magnitude of overhang increased with larger femoral component sizes among both sexes. Femoral component overhang of >or=3 mm approximately doubles the odds of clinically important knee pain two years after total knee arthroplasty.

Loosening and osteolysis with the press-fit condylar posterior-cruciate-substituting total knee replacement

Background: Aseptic loosening and osteolysis are rarely associated with cemented posterior-cruciate-substituting total knee replacements. Consequently, there is a paucity of information on this topic. Methods: After a mean follow-up interval of fifty-six months (range, thirty-seven to eighty-nine months), sixteen (2.9%) of 557 posterior-cruciate-substituting primary total knee replacements were revised by a single surgeon because of loosening and osteolysis. Clinical, radiographic, and retrieval analyses were conducted to determine the mechanism of loosening and to identify associated risk factors. Results: All sixteen knees (fifteen patients) were rated as good or excellent at one year after the primary replacement, with mean clinical and functional Knee Society scores of 95 and 86 points, respectively. Nine of the fifteen patients who had a revision because of loosening and osteolysis had had a total knee arthroplasty on the contralateral side compared with only 18% of the patients who did not have a revision (p = 0.026). No evidence of transmission of substantial anteroposterior stresses from the posterior-cruciate-substituting mechanism was found. All twelve retrieved knee implants, however, had damage to the lateral and medial side walls of the polyethylene posterior-cruciate-substituting post. Damage to the inferior surface of the polyethylene inserts had a rotational pattern, with the axis of rotation in the medial compartment. Surface damage in a rotational pattern was also present on the superior and inferior surfaces of the titanium tibial base-plates. Conclusions: In the knees in our study, rotational forces were generated by impingement of the side walls of the intercondylar box on the polyethylene post. Such box-post impingement can occur throughout the range of motion. Rotational stresses are transmitted to the modular interfaces and to the metal-cement interfaces, resulting in loosening and osteolysis. A reduction in rotational constraint would be desirable. Patients with bilateral total knee replacement may be at increased risk for this type of loosening.

Posterior cruciate function following total knee arthroplasty: A biomechanical study

The strain developed in the posterior cruciate ligament (PCL) of eight fresh cadaveric knees was measured before and after total knee arthroplasty using a loading technique that simulated stair ascent and descent. Each knee was instrumented with a Hall Effect strain gauge (Micro-Strain, Burlington, VT) in the PCL, a load cell in the quadriceps tendon, an electrogoniometer, and an array of linear displacement transducers to measure femoral rollback. Testing was undertaken with each knee in its normal state with the anterior cruciate cut and with a cruciate-retaining prosthesis, a cruciate-excising prosthesis, and a cruciate-substituting prosthesis. Normal PCL strain levels were produced in only 37% of the trials following implantation of the cruciate-retaining knee arthroplasties. With a cruciate-retaining prosthesis, femoral rollback decreased by an average of 36% and was associated with a 15% loss in extensor efficiency. In the procedures performed with excision of the PCL, rollback decreased by 70% and extensor efficiency by 19%. Cruciate substitution resulted in a 12% loss in rollback and an 11% decrease in extensor efficiency. The strain developed within the PCL during knee flexion was found to be extremely sensitive to the thickness of the polymeric tibial insert. In the majority of cases, it was not possible to restore normal ligament loading with flexion while simultaneously maintaining acceptable varus/valgus stability of the knee joint. Using a range of contemporary knee arthroplasties, the authors were unable to consistently reproduce normal function of the PCL.

Modular femoral offset stems facilitate joint line restoration in revision knee arthroplasty.

Restoration of proper joint line position in revision total knee arthroplasty is essential in promoting recovery of function. We retrospectively analyzed joint line restoration and clinical outcomes in 22 consecutive femur revision cases using modular offsets of variable length and direction between the intramedullary fixation rod and the femoral component. Flexion and extension gap balancing techniques and medial epicondylar referencing was used to achieve proper position of the joint line. Position of the reconstructed joint line from postoperative radiographs was compared to the baseline position of intended anatomic placement determined from pre-operative planning radiographs. Postoperative joint line height averaged 1.6 mm distal to baseline (range, 5 mm distal to 2.5 proximal). Joint line was restored to within 2 mm of anatomic position in 12 of the 22 knees. Sixteen patients received conventional, minimally constrained tibial inserts, and joint stability was achieved in all cases.Level of Evidence: Therapeutic study, Level IV (case series). See Guidelines for Authors for a complete description of levels of evidence.

Fixed Versus Rotating Platform Total Knee Arthroplasty: A Prospective, Randomized, Single-Blind Study

The purpose of this randomized, single-blind clinical trial was to compare a rotating platform (RP) total knee arthroplasty to a fixed-bearing (FB) total knee arthroplasty. Ninety-five knees in 69 patients were implanted by 2 surgeons. There were no significant differences in the preoperative demographics. At a minimum of 2-year follow-up, clinical outcomes and complication rates were similar, with the exception that the RP group had significantly better stair-climbing scores (P = .04). Postoperative range of motion was equally good in both groups (FB knees, 1°-125°; RP knees, 1-126°). There were no bearing dislocations in the RP group. In conclusion, this RP design performs at least as well as the FB version, and the RP patients reported better stair-climbing ability. Enthusiasm for this finding should be tempered by the relatively small sample size.

Modular insert exchange in knee arthroplasty for treatment of wear and osteolysis

Wear and osteolysis have been successfully treated by modular polyethylene exchange in revision hip arthroplasty. How ever, studies of the same approach in revision knee arthroplasty have not provided similar results. We evaluated the results of isolated polyethylene exchange for wear and/or osteolysis in 68 press-fit condylar TKAs from four centers. At a minimum of 24 months after polyethylene exchange surgery (average, 44 months; range, 24-83 months), there were 11 failures (16.2%). Failures included aseptic loosening in 10 knees and infection in one. With the relatively small cohort size we were unable to identify factors that predicted which knees were more likely to fail: we observed no correlation between failure and patient demographics, component design, or use of cement versus bone graft augmentation. Radiographic review demonstrated no progression of osteolytic lesions in 97% of knees in the study. While the short-term followup limits the conclusions, we believe the 84% success rate with modular polyethylene exchange for wear and osteolysis and the lack of progression of osteolytic lesions in the majority of the knees are encouraging. Full revision of well-fixed total knee components can lead to substantial bone loss, particularly in the face of osteolysis and we therefore consider modular polyethylene exchange in press-fit condylar knees a reasonable option for wear and osteolysis.Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence

Surface damage on open box posterior-stabilized polyethylene tibial inserts.

Twenty retrieved Scorpio® posterior-stabilized implants were available for analysis. The mean implantation time was 22 months (range, 2 days–42 months). Favorable types and amounts of surface damage were seen on the tibiofemoral and backsides of these modular PE liners that had been packaged in an inert environment and then sterilized by gamma irradiation. Delamination represented only 0.1% of the total surface damage. Off-axis loading (varus malalignment) was associated with tibial component loosening but there was no evidence of peripheral damage of PE caused by edge loading. With this open-box design, hyperextension marks on the anterior aspect of the posterior-stabilized post from femoral component impingement occurred in 11 of 20 cases and was related to sagittal component positioning: excess tibial slope or increased tibial slope combined with a flexed femoral component. Unique coarse abrasions occurred in 16 of 20 cases and were the result of cement extrusion into the open box, especially with varus malalignment. These observations provide guidance for optimizing the surgical technique and the design of posterior-stabilized total knee components.

The New Arthritic Patient and Arthroplasty Treatment Options

• Describe the indications for unicompartmental femorotibial knee arthroplasty • Describe the key technical points during surgery for patellofemoral replacement.