Flexion-extension gap changes during total knee arthroplasty: effect of posterior cruciate ligament and posterior osteophytes removal.

Flexion and extension gap heights were measured in 50 consecutive primary posterior-stabilized total knee arthroplasties (TKAs) to determine whether posterior cruciate ligament (PCL) release or re-establishment of the posterior condylar recess increased gap width. After PCL release, a slight symmetrical increase was noted in both gaps. In extension, gap width increased on average 1.3 mm and 1 mm in the medial and lateral compartments, respectively. The same pattern was observed in flexion, averaging 1.3 mm medially and 1.3 mm laterally. Another increase in the two gaps was observed after the posterior condylar osteophytes were removed and the posterior recess was re-established. The gaps in extension increased, with respect to the base-line value, on average 1.8 mm medially and 1.8 mm laterally, whereas flexion increased an average 2 mm medially and 2.2 mm laterally. No statistical differences were noted between flexion and extension gaps. No independent differences between the flexion and extension gaps were found in any surgical phase. Posterior cruciate ligament removal and re-establishment of posterior condylar recess does not require additional consideration in gap balancing during posterior-stabilized TKA.

Assessment of backside wear from the analysis of 55 retrieved tibial inserts.

Fifty-five retrieved tibial inserts with four different locking mechanisms were evaluated for evidence for polyethylene wear between the inferior surface of the tibial insert and metal tray. This type of wear will be referred to as backside wear. Backside wear was assessed by evaluating manufacturer's stamped markings on the inferior polyethylene surface. Because these markings are embossed into the polyethylene surface, they were used as indicators of backside wear. Decreases in the depths of markings indicated that backside wear was clearly evident, regardless of design, in 24 (44%) of the inserts. In eight of these 24 inserts, the manufacturer's stamped markings were removed completely. The amount of polyethylene wear was as a high as 591 mg from the inferior surface. This corresponds to a polyethylene wear rate from the backside of the tibial insert of greater than 100 mg per year, which is two to four times higher than wear rates associated with total hip replacements. The current work provides direct evidence of backside wear in all four tibial insert designs. Backside wear of tibial inserts can be a significant contributor to polyethylene wear in total knee arthroplasty. Close attention should be given to the fixation of tibial inserts to metal trays by manufacturers and surgeons.

Mobile bearings in primary knee arthroplasty.

Mobile-bearing knee arthroplasty (MBKA) has potential advantages compared with conventional fixed-bearing total knee arthroplasty (TKA). By allowing unconstrained axial rotation, MBKA can offer greater articular conformity without an increased probability of loosening due to increased axial torque. Increased articular conformity minimizes polyethylene contact stresses, thereby reducing linear wear and subsurface fatigue failure. Axial rotation of the platform also enables self-correction of tibial component malrotation. Despite these advantages, the long-term clinical results obtained with current MBKA devices are similar to those obtained with well-designed fixed-bearing TKA prostheses, with no data suggesting their superiority. The disadvantages of MBKA include bearing dislocation and breakage, soft-tissue impingement, a steep technique learning curve, and concerns about volumetric wear. Hypothetically, longer-term follow-up of MBKA results may reveal a significant difference from fixed-bearing TKA results as the fatigue failure threshold of incongruent polyethylene is exceeded.

Does modularity affect clinical success? A comparison with a minimum 10-year followup.

A comparison of the clinical and radiographic results of patients with metal-backed monoblock Insall-Burstein I and modular Insall-Burstein II Posterior Stabilized Knee Prostheses was done. The minimum followup was 10 years. The clinical results were comparable with a similar average Hospital for Special Surgery knee score of 85 and 84 points, respectively. Likewise, the Knee Society Knee and Functional Scores showed no statistical difference. Radiographically, the incidence of minor radiolucent lines was 11% for the Insall-Burstein I prostheses and 29% for the Insall-Burstein II prostheses, but their presence was of no clinical significance. There was no clinical or radiographic evidence of tibial component loosening with either prosthetic design and there were no revisions for polyethylene wear or osteolysis in either cohort of patients.

Mobile-bearing knee replacement: concepts and results.

In summary, if TKRs are to be performed in patients who are younger and more active than those who had the initial procedures in the 1970s and 1980s, better wear performance is imperative for long-term durability, especially if surgeons continue to consider the versatility associated with modular knee-replacement systems to be a necessity. At least with some designs, including the Oxford knee and the LCS knee, the results after a minimum follow-up of 10 years are comparable with the best results after arthroplasty with fixed-bearing designs in terms of wear, loosening, and osteolysis (Table 7). As with fixed-bearing designs, there are additional challenges in terms of optimizing bearing-surface conformity and improving kinematics. Improvements in future designs of mobile-bearing total knee replacements should include better control of bearing mobility patterns to reduce the prevalence of the abnormal kinematic motions that have been observed in fluoroscopic evaluations.

Accuracy of soft tissue balancing in total knee arthroplasty.

To the best of our knowledge, this is the first study to assess the accuracy of balancing of the flexion and extension gaps in total knee arthroplasty (TKA). Measurements of the heights of the flexion and extension gaps were obtained during 104 consecutive primary, posterior-stabilized TKAs in osteoarthritic patients. Clinically, all knees appeared to be well balanced intraoperatively. Rectangular flexion and extension gaps almost always were obtained within 1 mm (84%-89%). None of the knees was >3 mm from being perfectly rectangular. Equality of the flexion and extension gaps was more difficult to obtain (47%-57% were within 1 mm). With meticulous attention, perfect soft tissue balance is not always achieved in TKA.

Primary constrained condylar knee arthroplasty for the arthritic valgus knee.

The purpose of the current study was to review results of primary constrained condylar knee arthroplasty in elderly patients with genu valgum deformity. The hypotheses were: (1) constraint has no adverse effects in elderly patients; (2) treating deformity with a constrained condylar knee prosthesis in lieu of lateral ligament release avoids morbidity, particularly peroneal nerve palsy and flexion instability; and (3) press-fit noncemented stem extensions enhance fixation of the cemented core components and are not prone to loosening. Between 1988 and 1993, 44 consecutive primary Constrained Condylar Knee prostheses were implanted in 37 patients (average age, 72.7 years) with an average valgus angle of 17.6 degrees. Indications for the Constrained Condylar Knee implant were: elderly patients with genu valgum deformity and medial collateral ligament incompetence. Outcome was assessed prospectively using the Hospital for Special Surgery and Knee Society scoring systems; followup was by independent observer. Clinical and radiographic followup (average, 7.8 years) was available for 28 knees (26 patients). The Hospital for Special Surgery score improved from 52.2 to 89.6 points. The average Knee Society score and functional scores improved from 27.4 and 32.4 points to 95.2 and 67.2 points, respectively. At followup, the average alignment based on anteroposterior radiographs obtained with the patient weightbearing was 5.3 degrees. No radiographic loosening, prosthetic failures, peroneal nerve palsies, or flexion instability occurred. No failures occurred in the 11 patients (16 knees) who died before the latest followup. To the authors' knowledge, this is the largest reported series with the longest reported followup of patients with primary Constrained Condylar Knee prostheses. The use of the Constrained Condylar Knee prosthesis for elderly patients with low physical demands with genu valgum resulted in significant pain relief and improved function.

Anatomy of the epicondyles of the distal femur: MRI analysis of normal knees.

Knowledge of precise anatomic landmarks and relationships of the distal femur can be helpful in knee surgery, especially primary and revision total knee arthroplasty. We analyzed 104 consecutive routine knee magnetic resonance imaging studies to define useful landmarks and relationships. The epicondyles are described, and the relationship of the epicondyles to the joint line is defined in multiple planes. Some significant gender differences were noted. The distance from the epicondyles to the joint line correlates with the transepicondylar width of the distal femur. This information can be helpful in determining appropriate joint line position intraoperatively. The posterior condylar angle averaged 3.11 degrees for all patients, and a tendency for the posterior condylar angle to increase with age was noted, but further study of this tendency is needed.

Revision total knee arthroplasty: a surgical technique.

The etiology of surgical failure should be defined before revision total knee arthroplasty (TKA) is contemplated, since revision surgery without a clear reason may fail to correct the underlying problem. The causes of mechanical failure include component loosening, instability, polyethylene wear, component malposition, extensor mechanism dysfunction, and loss of motion. Revision that is required because of an infection is also acomplex situation, which requires skill and meticulous technique in order to restore a functional outcome. A successful revision needs to account for ligamentous balance, bone loss, alignment, and fixation.

The posterior condylar angle in osteoarthritic knees.

The posterior condylar angle is formed by the transepicondylar axis and the tangent line to the posterior condyles. It is an important relationship to determine rotational alignment of the femoral component in total knee arthroplasty. We measured this angle directly in 107 osteoarthritic knees undergoing total knee arthroplasty. The posterior condylar angle was significantly greater in valgus knees than in other osteoarthritic knees. Given the standard deviations and ranges of values noted, the posterior condyles are potentially unreliable references for femoral component rotation in some knees.

Primary total knee arthroplasty in stiff and ankylosed knees.

This study reviewed 71 patients who underwent 82 total knee arthroplasties between 1974 and 1987. All patients had severe limitations of motion preoperatively with a total preoperative arc of motion of < or = 50 degrees. Follow-up ranged from 2 to 12 years (average: 5.3 years). The average preoperative knee score was 38 (range: 14 to 54). The average preoperative arc of motion was 36 degrees (range: 0 degree to 50 degrees), with an average flexion contracture of 22 degrees average maximum flexion of 58 degrees. Postoperatively, the average knee score was 80 (range: 0 to 98). The average postoperative arc of motion was 93 degrees (range: 35 degrees to 130 degrees), with an average maximum flexion of 94 degrees. Nine knees had 5 degrees flexion contractures, while 5 knees had 10 degrees flexion contractures. Postoperatively, no knee had a flexion contracture > 10 degrees. Two knees had a decreased range of motion postoperatively. Two knees with severe flexion-valgus deformities developed peroneal nerve palsies that both resolved. Total knee arthroplasty in stiff or ankylosed knees can produce good or excellent results and can lead to significant improvement in range of motion and pain.

Total knee arthroplasty in patients who were obese with 10 years followup.

The 10-year results of primary total knee arthroplasty in patients who were obese were evaluated. In a 2-year period, 120 patients had 165 primary, posterior stabilized, cemented total knee replacements with metal backed tibial components. After exclusions, 56 patients (73 knees) were available for study. Twenty-two patients (32 knees) were classified as obese, and 34 patients (41 knees) were classified as nonobese. At 10 years followup, patients who were obese had lower Knee Society function scores than had the patients who were nonobese (mostly attributable to more difficulty with stair climbing). Patients who were obese had poorer patellar scores at 10 years. Bilaterality was more common in patients who were obese and preoperative knee scores were lower. Minor nonprogressive radiolucent lines were seen more commonly in the patients who were obese. Overall, however, 10-year Hospital for Special Surgery scores and Knee Society scores for patients who were obese were comparable with scores for patients who were nonobese and given lower preoperative Hospital for Special Surgery scores, improvement in knee score was greater. Revision rates in patients who were obese were not higher than in patients who were nonobese at 10 years followup. More study is needed of the subgroup of patients who were morbidly obese.