There have been various reports of structural or cancellous allograft with acetabular cages in the treatment of chronic pelvic discontinuity.5, 6, 17 On the whole, literatures indicate mechanical constructs like cages appear to provide unreliable outcomes, given the potential for fatigue and late loosening. Therefore, it’s critical to achieve initial mechanical stability for bone ingrowth to occur into the prosthesis both superiorly and inferiorly to bridge the discontinuity in a biologic fashion. Both cup-cage construct and CTAC showed promising survivorships.6, 8 However, the extensive soft tissue dissection necessary for implantation of these constructs may predispose the hip to instability and increase the risk of deep infection and nerve injury. The jumbo cup combined with acetabular distraction technique, by contrast, may be a more feasible option.
Only one of our 12 patients treated with the acetabular distraction technique required revision due to acetabular component loosening. Similarly, early migration of the acetabular component was encountered in the study by Sheth et al.10 They achieved stability in a new position and remained pain free. The loosed cup in our study migrated to a more steep orientation. Asymptomatic though she is, she has to face the high risk of accelerated wear and dislocation. The failure of ingrowth of the acetabular cup might be attributed to killing effect of pelvic radiation. According to the short-term results by Berry et al18, structural allograft with cage reconstruction was more suitable for irradiated bone than cementless cup. Thus it can be inferred that adequate contact with live host bone is the prerequisite of application of jumbo cup with acetabular distraction. No migration of the component was detected in the remaining patients. In a two-center radiological analysis by Sheth et al10, 69% (22/32) of patients demonstrated radiographic evidence of healing of the discontinuity at the time of final follow-up, which could be attributed to the effect of central compression across the discontinuity achieved by acetabular distraction technique. However, in our series, there is not enough to make connections between bony callus formation and healing of the discontinuity in the X-ray.
Reconstruction of chronic pelvic discontinuity with extensive bone loss is fraught with difficulty and complications. Compared with cup-cage construct and CTAC, jumbo cup combined with acetabular distraction technique is associated with decreased surgical time and minimization of soft tissue stripping. We did not encounter any complications. It may have something to do with the small size of our series. The distraction technique did have some complications, such as femoral artery injury, bowel injury, sciatic nerve palsy, superficial infection, dislocation and hematoma, as described by Sheth et al.10 However, the frequency of each complication was relatively lower compared with other methods6, 8, especially the rate of dislocation and infection. It is worth noting that all neurovascular injuries occurred in their original cohort of patients undergoing acetaular distraction. At that time, implanted acetabular cup was selected to be 6 mm to 8 mm larger than the last reamer, and the acetabulum may have been overdistracted, resulting in stress transfer to the adjacent neurovascular structures.9
Our method of distraction is more similar to their refined technique. 10 The appropriate sized reamer was defined as allowing the surgeon to move the patient’s pelvis as a unit by moving the handle. And the acetabular component chosen for implantation was the same size as the last reamer. But we do not use a dedicated extra-acetabular distractor. We consider that osteoporosis is common among Asian patients with chronic pelvic discontinuity. A stiff device will probably cause further damage to the pelvis. To avoid inadequate distraction secondary to excessive discretion, we should ensure that pelvis can be moved as a whole, without micromotion.
In some cases of severe segmental bone defect, jumbo cup with acetabular distraction technique may be not enough to achieve stability. In our study, augment was used in two patients, and cup-cage construct was used in five patients. In fact, as a supplementary measure, the acetabular distraction technique was described by some authors.6, 19 Namely, acetabular distraction technique itself can further secure the component by the fibrous recoil. However, perhaps under some circumstances, the acetabular reconstruction cannot do without the support of a porous metal cup and augments, and even an overlying titanium cage.
There are five limitations in our study. First, our series is relatively small due to the low incidence of these difficult cases. Second, with the same reason, there is no control group for comparison with other techniques. Third, the followup is not long enough, which makes the long-term durability of this technique pending. Fourth, the retrospective design of this study is a discernable limitation. Fifth, we did not assess intraobserver variability for assessing radiographs.