High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement

Abstract

We have examined the results obtained with 72 NexGen legacy posterior stabilised-flex fixed total knee replacements in 47 patients implanted by a single surgeon between March 2003 and September 2004. Aseptic loosening of the femoral component was found in 27 (38%) of the replacements at a mean follow-up of 32 months (30 to 48) and 15 knees (21%) required revision at a mean of 23 months (11 to 45). We compared the radiologically-loose and revised knees with those which had remained well-fixed to identify the factors which had contributed to this high rate of aseptic loosening. Post-operatively, the mean maximum flexion was 136 degrees (110 degrees to 140 degrees) in the loosened group and 125 degrees (95 degrees to 140 degrees) in the well-fixed group (independent t-test, p = 0.022). Squatting, kneeling, or sitting cross-legged could be achieved by 23 (85%) of the loosened knees, but only 22 (49%) of the well-fixed knees (chi-squared test, p = 0.001). The loosened femoral components were found to migrate into a more flexed position, but no migration was detected in the well-fixed group. These implants allowed a high degree of flexion, but showed a marked rate of early loosening of the femoral component, which was associated with weight-bearing in maximum flexion.

Range of motion and function are similar in patients undergoing TKA with posterior stabilised and high-flexion inserts

“…Nagura et al found that deep-flexion activities generate one to 13 times larger net quadriceps moments (average five) than does walking [25]. This may increase patellofemoral joint stresses, with the potential for causing pain, excess wear, patellar fracture, and loosening [9,32]. Han et al reported a 38% prevalence of femoral component loosening in the LPS HF TKA at a mean follow-up of 2.7 years in patients engaging in weight-bearing, high flexion activities [9].…”

“…This may increase patellofemoral joint stresses, with the potential for causing pain, excess wear, patellar fracture, and loosening [9,32]. Han et al reported a 38% prevalence of femoral component loosening in the LPS HF TKA at a mean follow-up of 2.7 years in patients engaging in weight-bearing, high flexion activities [9]. Some HF femoral components also require a larger bone resection [32,33].…”

2009 Marshall Urist Young Investigator Award: How Often Do Patients with High-Flex Total Knee Arthroplasty Use High Flexion?

“…A third study reported no difference in average postoperative knee flexion in 50 patients who underwent bilateral TKAs (138°for NexGen 1 LPS-Flex versus 135°for NexGen 1 LPS) [26]. To date, three of nine clinical studies suggest patients have increased postoperative flexion with highflexion prostheses [6,19,20,23,26,38,42,44,45]. One of these studies reported patients with maximum flexion greater than 135°had a better functional WOMAC Osteoarthritis Index score than patients with maximum flexion of 135°or less (17.5 versus 14.3) [45].…”

“…These high stresses may lead to pain, increased wear, fracture, and increased patellar loosening. One study of high-flexion TKAs reported a 38% rate of aseptic loosening at 32 months followup [20]. What is not known currently is how often patients will use, during daily activities, any additional safe flexion provided by the high-flexion TKA.…”

Editorial Comment: 2016 Knee Society Proceedings

“…There are many examples in the long history of orthopaedics demonstrating that slow, gradual incorporation of new technology is advisable. It is important to remember the unforeseen consequences of certain metal-on-metal hip resurfacing and replacement designs [6], the early failure of new bone cement formulations [1,4], and the unpredicted failures of even fairly minor modifications to successful products, including certain ''high flex'' femoral component designs [3]. Orthopaedics certainly is not alone in having suffered such repercussions of untested new technology-novel pacemakers [2] and cochlear implants [5] are just two examples that come to mind from outside our specialty.…”