Improvement in hamstring and quadriceps muscle strength following cruciate-retaining single radius total knee arthroplasty.

backgroundThe ability to reach full functional capacity following total knee arthroplasty (TKA) is reliant on the strength of the quadriceps and hamstring muscles. Weakness of these muscles can persist anywhere from 1 to 3 years post-operatively. There remains considerable controversy as to what factors influence restoration of muscle strength after TKA. Implant designs have been implicated in the ability of patients to recover. Currently there is a paucity of literature available describing the influence of patient characteristics, surgical factors, and clinical outcomes on quadriceps and hamstring muscle strength following TKA with a cruciate-retaining, single radius (SR) implant. For this reason, we sought to investigate TKA patients for: (I) quadriceps muscle strength; (II) hamstring muscle strength; (III) flexion/extension (F/E) ratio; (IV) clinical outcome scores; (V) influence of patient characteristics on muscle strength at one-year post-operatively.

methodsA review of TKA patients who were assessed for hamstring and quadriceps muscle strength was conducted. A total of 39 patients (26 men and 13 women), who had a mean age of 68 years (range, 51 to 88 years) were included. Isokinetic dynamometer testing at 180 degree/second for 3 sets of 10 repetitions in extension and flexion were performed by an independent physical therapist to assess dynamic concentric torque of the hamstrings and quadriceps muscle. F/E ratios were calculated. TKA was performed via subvastus (n=20) or midvastus (n=19) approach. Subgroup analysis for surgical approach, concomitant spinal pathology (n=11), gender, age and body mass index (BMI) were performed. Knee Society Scores (KSS) and range of motion (ROM) were assessed at each visit. Comparisons of groups were performed using paired

resultsMean postoperative relative extension torque was 23 Nm/kg (range, 9 to 43 Nm/kg), representing a mean increase of 38% (range, -16% to 100%; P=0.0267) from pre-operative status. A mean increase of 27% (range, -15% to 100%; P=0.0433) in flexion strength and mean relative flexion torque of 19 Nm/kg (range, 8-37 Nm/kg) was observed. Pre-operative mean F/E ratio was 0.8 and 0.9 post-operatively (P=0.3028). Men demonstrated significantly greater improvements in flexion compared to women (22%

conclusionsRestoration of quadriceps and hamstring muscle strength can be expected at 1 year post-operatively regardless of gender, surgical approach or concomitant spinal pathology. Further comparative investigation on the impact of implant design on hamstring and quadriceps muscle strength is warranted. However, the use of a SR, CR TKA system demonstrated significant improvements post-operatively in quadriceps and hamstring strength.