ETO is useful in THR infection treatment in two-stage revision surgery where femoral components could not be extracted with standard techniques. It is associated with a infection resolution rate of 87%, and union rate reported to be at 95% at 11.5 weeks [19] and at 98% at 4 months. Superior GT migration less than 5 mm was reported in 7% of ETOs, while early loosening was reported to be at 1.3% at 4 months after operation. Complications also included osteotomy fragment fracture in 5.4% [19].
While in aseptic single THA revision, overall union rate was reported to be at 93.1%, and the rate of femoral stem subsidence > 5 mm was 7.1%, the results were similar between THA revisions with ETO for periprosthetic fractures and THA revisions with ETO for reasons other than fracture. Older age and prior femoral cementation may be negative factors in ETO union rates [23]. Persistent pain and painful hardware can also occur as postoperative complications; other complications include posterior dislocation, traumatic periprosthetic fracture [25].
Seung-Jae Lim et al., in 2011, compared a cohort of non-infected patients who received revision hip arthroplasty using ETO with a periprosthetic hip infection group. The hip infection group had infection eradication rate of 96%, a union rate of 100% at 10.6 weeks, rate of proximal migration > 2 mm of 8%, a rate of intraoperative femoral crack of 13%, a rate of femoral stem subsidence > 5 mm of 4%, a periprosthetic fracture rate of 8%, and a dislocation rate of 4%. The non-infection group reported a 96% union rate at an average of 10.4 weeks, a rate of proximal migration > 2 mm of 8.6%, an intraoperative femoral crack rate of 10.8%, a rate of subsidence > 5 mm of 8.6%, a periprosthetic fracture rate of 4%, and a dislocation rate of 2% [13].
Similar findings were observed in a study of a mainly single-stage cementless ETO revision hip arthroplasty involving 166 patients, with a union rate of 98.8% at 2-year follow-up. In the study, 71% united within 3 months, 0.6% had malunion, 1.2% had proximal segment migration > 2 mm, 2.4% had fracture of osteotomy fragments, 92.1% had bony ingrowth 2-years after operation, 10.2% had dislocation and 10.2% received a re-operation [24].
When using fluted and tapered modular distal femur fixation stem with or without extended trochanteric osteotomy, the rates of cortical perforation and marked stem subsidence > 5 mm were significantly higher in the group treated without an ETO. However, when stratified in terms of bone defect, no significant difference was found [10].
Delayed extended trochanteric osteotomy fixation in two-stage cemented arthroplasty with interval placement of antibiotics-impregnated cement spacer is associated with a high union (up to 100%) rate at 6 months, and a subsidence rate of 15%. Delayed ETO fixation with interval placement of articulating antibiotic-impregnated cement spacer permits reliable healing of the osteotomy [12].
Antibiotic-coated prostheses (ACP), such as Zimmer-Biomet Stage One Select Femoral Spacer (ZBSO) used in stage-1 revision surgery in the setting of ETO like moulded or hand-made spacers have high rate of spacer fracture, with ACP spacer fracture rate being at 25% due to its thin core, compared to a rate of 2.4% without ETO. This implant should be used with caution with an ETO, and an alternative ACP should be considered when performing ETO [26].
A comparison between ETO length (average at 14.7 cm), and modified sliding trochanteric osteotomy length (average at 6.1 cm) has shown that the length of osteotomy is negatively correlated to the GT migration distance [27]. Hence, osteotomies shorter than 10 cm are at high risk of developing over 1 cm GT proximal migration, especially without adequate distal cerclage wire fixation [5]. Sliding trochanteric osteotomy has a non-union rate 4 times the non-union rate observed in ETO cases, [28] at least partly due to its decreased length.
Cortical strut allograft with ETOs can be used in cases where bone stock restoration is needed with no significant difference in functional outcome, subsidence, alignment or migration. There is an insignificant lower union rate with the use of cortical strut allograft. In mild to moderate cases of bone stock loss (Paprosky grade I & II), excellent clinical outcome and high union rate were reported in ETOs without strut augmentation [29].
The use of cerclage wire with ETO does not seem to be related to reduced infection eradication rate or reduced osteotomy union in the first stage of a two-stage revision surgery for chronic infection [11].
Fixation of the ETO using 3 or 2 cables showed no significant difference in stiffness, peak force, or displacement in biomechanical model [30].
At 1 year follow-up, there was some evidence that union rate of ETOs was higher with trochanteric metallic reinforcement plates (MRP plate) compared to cables and metallic wires [31].
The main limitation of the case series study is that it mainly relied on radiographic measures and had limited functional outcome assessment. Another limitation from the literature review is that there was evident disparity in the follow-up periods, ranging between 1 year to several years, while this lack of uniformity did not generally affect the shorter-term outcomes, it can affect some long-term conclusions derived from these results.
