There is a high risk of arthritis in the contralateral hip joint in patients with below knee amputations [19,20,21]. Kulkarni [20] et al. analyzed 44 cases of below knee amputations and reported that 18% of patients developed arthritis in the contralateral hip joint; this was double the incidence observed in non-amputated patients. Struyf et al. reported that hip arthritis on the contralateral side of the amputated leg was five- to ten-times higher and the progression of the arthritis was faster in patients with amputations than in those without [21]. The most common cause of arthritis in the contralateral hip joint in patients with below knee amputation was a change in their gait pattern owing to special circumstances, such as leg amputation and use of prosthetics (increased metabolic energy expenditure, decreased walking speed, larger stride width, shorter stride length with the intact limb, and increased stance time). It is known to induce pain and degenerative changes by inducing a higher load on the joint owing to an increase in the ground reaction forces. [2, 20, 22,23,24] The gluteus medius muscle is an important abductor muscle [25] that plays important roles in stabilizing the pelvis during the period of single support of the gait cycle [22], and in the balance and normal movement of the pelvis and lower limb during gait [26]. The role of the muscle abduction in the hip contralateral to the amputated leg becomes particularly more important for stable gait in patients with leg amputations. In this case, the anterior approach was used and the anterior part of the gluteus medius—which plays a major role in abduction, internal rotation, and flexion of the hip joint—was cut off [27]. Patients who underwent the anterior approach showed more falls within the postoperative 3 months, and slower functional recovery compared to those who underwent the posterior approach. Therefore, it was thought that damage to the anterior part of the gluteus medius by the anterolateral approach may have affected the outcomes.
The incidence of periprosthetic femoral fractures after hip arthroplasty is increasing [28]. A recent study showed that the incidence of periprosthetic femoral fracture is approximately 1% after primary HA [29]. The authors observed a higher incidence of periprosthetic femoral fractures in both groups (3% in the PA group (1 in 33 patients) and 8.8% in the ALA group (3 in 34 patients)). It is a well-known fact that a patient with amputation belongs to the high-risk group for fall [30]. Falls occurred more frequently in the ALA group (2 out of 3 patients) than in the PA group within 3 months after the operation. We believe that the delayed functional recovery of the ALA group (until 3 months postoperative) seems to be related to these results and the damage of the anterior fiber of the gluteus medius during ALA.
In a study of functional recovery based on the approach type, Jeya et al. [31], in a medium term (5 years), found no difference in the clinical benefit of surgery as defined by the change in Oxford Hip Score or in the absolute postoperative Oxford Hip Score between patients who underwent PA and with those who underwent ALA. However, the initial difference at 1 year in Oxford Hip Score between the PA and ALA groups may be attributed to the increased trochanteric pain [32] and increased gait abnormalities [33] in the ALA group during the immediate postoperative period. In particular, Pfirrmann et al. [32] found changes in the abductor muscle after hip arthroplasty using MRI. In the case of HA with partial incision of the gluteus medius and gluteus minimus, defects in the gluteus minimus and gluteus medius were observed in 8 and 16% of patients without postoperative trochanteric pain or limp symptoms, respectively; however, gluteus medius and gluteus minimus defects were found in 62% and in 56% of patients with symptoms such as trochanteric pain or limp, respectively. In the present study, functional recovery was lower in the ALA group than in the PA group until 3 months postoperatively, but no significant difference was observed between the two approaches from 6 months to the last follow-up. Therefore, we concluded that when HA is performed to the contralateral side hip joint of amputees, minimizing the gluteus medius damage and doing the best to repair it was necessary when using the ALA.
Amputees are a high-risk group for fall. Kulkarni et al. found that 60% of amputees reported that falling affected their daily life, work, leisure, and confidence [30]. These falls are due to altered lower limb mechanics; therefore, transtibial amputees make compensatory gait adjustments. In the present study, gluteus medius muscle damage in patients with high-risk falls could be an important risk factor for falls and PPF in the ALA group within 3 months after surgery.
Other notable findings are those of four patients with PPF (around the femoral stem) and of two patients with dislocation due to prosthetic leg-related falls, despite the absence of osteoporosis or problems with walking ability. Therefore, providing thorough education to patients to wear and use the prosthesis with caution after surgery is important. Since ALA and PA both have advantages and disadvantages, we do not believe that only one approach should be used exclusively for hip arthroplasty in the contralateral hip joint of below the knee amputees. However, the following points should be considered before surgery. First, it is important to use the approach that is the surgeon is most familiar with. Surgeons using ALA should minimize the damage of the gluteus medius muscle and the muscles around the hip joint and should operate quickly and safely. Surgeons using PA should reduce damage and do their best to repair structures that could affect the stability of the hip joint, such as the short external rotator. Second, as our results have shown, the risk of falls should be adequately explained to patients as there is a high risk of falls and fractures around the femoral stem in amputees compared with non-amputees. In particular, patients with ALA should be more careful because if they fall within the first 3 months after surgery they will have a slow recovery of gait ability. Last, patients with a high risk of falls (those living on the floor, those not expected to be well coordinated with postoperative care, those who need to return to active work soon after surgery, etc.) should have PA performed by a skilled surgeon.
This study has some limitations. First, the sample size is small. However, collecting data from many cases is difficult because hip arthroplasty of the contralateral side hip joint in patients with below knee amputation is rare. Second, the surgery was performed by 4 surgeons all of whom have > 10 years of experience with total hip arthroplasty and have performed > 300 surgeries per year. Third, the difference in muscle strength due to the injury to the gluteus medius, which was the most significant difference between the two approaches, was not identified. It was evaluated by comparing only events of falling or functional recovery. The study was further limited by its retrospective nature and the relatively small number of patients. Therefore, the results need to be supplemented by large-scale prospective studies. The final limitation is that the study included both patients with total hip replacement and with hemiarthroplasty. In particular, 9 out of 10 hemiarthroplasty patients had hemiarthroplasty due to femoral neck fracture. Most patients with femoral neck fracture were elderly and likely to have osteoporosis and often had reduced gait ability before fracture. Yet, because we selected patients who were socially active with prosthetics before the fracture, they were included in the study. It is, however, considered that a limitation of this study was the failure to distinguish the presumed complications that are more likely to occur in total replacement, such as dislocation.
