We retrospective analyzed prospectively collected data of 294 patients underwent HF-TKA between January 2001 and December 2009. Among 294 patients, 34 patients were excluded (seven patents died and 27 were lost to follow up), leaving 260 patients for this study (88.4 %). Decision for HF-TKA were based on considering their preoperative ROM, life style and activity level, knee alignment, deformities, patient expectation after surgery . We performed HF-TKA for patients with preoperative maximal flexion more than 100° or more. There were 212 women and 48 men with age of 69 years (range, 57–83 years) at the time of surgery. The body mass index was 27.0 kg/m2 (range, 20.5–34.1 kg/m2). Minimum follow-up was 5 years (mean, 6.7 years; range, 5–13 years). This study was performed with the approval of the institutional review board of our hospital (Samsung Medical Center 2014-01-065). All participants gave their written informed consent to assessing and using their data.
The senior author (C-WH) of this study performed all the TKAs using standardized technique as described elsewhere . The cement was applied directly on the anterior flanges and distal cut surface of femur and on the posterior facet of the femoral component . Posterior femoral osteophytes were carefully removed with knee in full flexion to aid in increased postoperative flexion. Patella was not resurfaced in this cohort. All surgeries in our study were done using NexGen Legacy Posterior-Stabilized Flex fixed bearing implant (Zimmer, Warsaw, IN, USA). The same postoperative rehabilitation program was used for all patients. Briefly, a closed suction drain was used for 2 days, and ankle pump exercises were commenced immediately after surgery. On the second postoperative day, a continuous passive motion machine was applied at a range of motion tolerated by the patient, and ambulation with a walker was encouraged. Patients were also encouraged to perform active and assisted knee flexion, and quadriceps setting exercises, and straight leg raising exercise against gravity. After the rehabilitation period, HF activities were allowed as tolerated. Even weight-bearing HF activities, such as, squatting and kneeling were not prohibited, if patients needed to perform these activities.
Patients were followed up at 1, 3, 6 months, 1 year after surgery and annually thereafter. Clinical outcomes were evaluated using ROM, American Knee Society knee scores (KSKS) and function scores (KSFS), and Western Ontario and McMaster Universities osteoarthritis index (WOMAC) scores. Non weight bearing passive flexion angles were measured in the supine position by independent examiner and calculated using two reference lines, a femoral line (from the lateral epicondyle of the distal femur to the tip of the greater trochanter) and a line from the tip of the fibula head to the tip of the lateral malleolus. Functional outcomes for HF activities were evaluated using a self-administered questionnaire (in accordance with 5-point Likert scales based on difficulty, 0–4 with zero being no discomfort and four being extreme difficulty), which consisted of seven HF activities that addressed whether the operated knee permitted HF related activities, such as, ascending and descending stairs, sitting or rising from a low chair, sitting or rising from the floor, cross-legged sitting, squatting, and kneeling . Responses to each question were scored according to five grades of difficulty for a particular activity (Grade 0: no difficulty, grade 1: mild difficulty, grade 2: moderate difficulty, grade 3: severe difficulty and grade 4: extreme difficulty (unable to do)). Levels 0, 1, and 2 were considered positive responses and levels 3 and 4 were considered negative responses.
For identifying aseptic loosening, radiographic evaluations were done based on the American Knee Society roentgenographic evaluation and scoring system. Full length and standing anteroposterior, lateral and Merchant’s view were acquired at each follow-up visit, and assessed for limb alignment, component positioning, and for any features of loosening. Widths of radiolucent lines were measured along the seven zones on lateral radiographs of the femur, seven zones on anteroposterior radiographs of the tibia, and three zones on lateral radiographs of the tibia. Any radiolucent lines identified were compared with the previous follow-up x-rays to classify them as progressive or non-progressive lines. Aseptic loosening is defined as radiolucency greater than 2 mm width, interval increases in the width of an existing radiolucency, cement fracture, and prosthesis migration . A comparison was also made between two groups (HF group and Non-HF group) divided based on their responses to squatting and kneeling (two of the most important weight bearing HF activities done in Asian population) for evaluation in loosening rates and functional scores. Both squatting and kneeling activities are known to impose high contact stress at the posterior articular surface in both normal as well as replaced knee , hence if at all the concept of HF activities leading to aseptic loosening is valid, the patients doing these activities will be affected first.
Paired t-test was used to determine the difference between preoperative and postoperative values of all continuous outcome variables (ROM, KSKS, KSFS, and WOMAC). To evaluate the effect of HF activities on the aseptic loosening, we grouped patients according to feasibility of squatting and kneeling (HF group and non-HF group). A Fisher’s exact test was used for finding any statistically significant difference in radiographic loosening rates between HF group and non-HF group. Independent t-test was used for comparison between the two groups. The significance level was set at 0.05. All statistical analyses were performed with SAS 9.3 (SAS Institute, Cary, NC, USA).