Abstract
Background
Fretting corrosion at the junction of the modular head neck interface in total hip arthroplasty is an area of substantial clinical interest. This fretting corrosion has been associated with adverse patient outcomes, including soft tissue damage around the hip joint. A number of implant characteristics have been identified as risk factors. However, much of the literature has been based on metal on metal total hip arthroplasty or subjective scoring of retrieved implants. The purpose of this study was to isolate specific implant variables and assess for material loss in retrieved implants with a metal on polyethylene bearing surface.
Methods
All 28mm and 32 mm femoral heads from a 12/14 mm taper for a single implant design implanted for greater than 2 years were obtained from our institutional implant retrieval laboratory. This included n = 56 of the 28 mm heads (−3: n = 10, +0: n = 24, +4: n = 13, and +8: n = 9), and n = 23 of the 32 mm heads (−3: n = 2, +0: n = 8, +4: n = 1, and +8: n = 6). There were no differences between groups for age, gender, BMI, or implantation time. A coordinate measuring machine was used to acquire axial scans within each head, and the resulting point clouds were analyzed with a custom Matlab program. Maximum linear wear depth (MLWD) was calculated as the maximum difference between the material loss and as-machined surface. Differences in MLWD for head length, head diameter, stem material, and stem offset were determined.
Results
Within the 28 mm head diameter group, there was no difference (p = 0.65) in MLWD between head lengths (−3: 4.0 ± 1.7 µm, +0: 10.4 ± 15.2 µm, +4: 4.4 ± 1.7 µm, +8: 4.3 ± 1.8 µm). There was no difference (p = 0.12) between the 28 mm (6.7 ± 10.9 µm) and 32 mm (5.5 ± 6.2 µm) head diameters. There was also no difference (p = 0.97) between titanium (7.3 ± 11.4 µm) or cobalt-chromium (5.9 ± 5.6 µm) stems, and no difference (p = 0.20) between regular (7.0 ± 10.0 µm) or high-offset (5.7 ± 8.0 µm) stems.
Discussion
The development of fretting corrosion at the head neck junction of metal on polyethylene total hip replacements is of substantial clinical importance. In a single taper design, head diameter, head length, stem material and stem offset were all not found to be contributory to magnitude of wear depth. This is in contrast to current literature, which is controversial regarding the role of head diameter, but head length is thought to be contributory. However, as this study using precise tools does not illustrate these proposed biomechanic factors of fretting corrosion, other factors influencing tribocorrosion such as trunnion surface finish, flexural rigidity, interface geometry and biochemical factors may need to be considered.
