gms | German Medical Science

Objectives: Complex revision hip arthroplasty is often needed to restore hip joint function when severe acetabular distortion or bone loss are present. The mirroring of the contralateral hemipelvis has been previously used to measure hip joint parameters of these complex cases. However, this technique cannot be applied when the contralateral hemipelvis is diseased or replaced. Statistical shape modelling (SSM) can help overcome a major challenge in the surgical planning of hip reconstruction and implant design by predicting anatomical information that is missing or impossible to capture with traditional modelling.

We aimed to aid the surgical planning of complex hip surgery. Our primary objective was to apply SSM to patients who previously underwent hip revision surgery.

Methods: This was a retrospective cohort study involving 42 patients with Paprosky type II, III defects and Crow type IV developmental dysplasia of the hip (DDH). An SSM was built on 50 healthy pelvises and used to virtually reconstruct the native pelvic morphology for all cases. Within the Paprosky type IIIB cohort, 18 of the 42 patients had a healthy contralateral side. The SSM-based models were then compared to the preoperative computerised tomography (CT) based reconstructions. The outcome measures were the difference in centre of rotation (CoR) between the SSM and 1) the diseased hip, 2) contralateral healthy hip (where present).

Results and conclusion: The largest difference in CoR was found between the hips with Paprosky defects and their corresponding SSMs (1), with a median of 22 mm (interquartile range [IQR]: 34–20 mm). The median difference in CoR between the SSM and the healthy contralateral side (3) was 8 mm (IQR: 10–5 mm).

The CoR of the dysplastic hips was found to have deviated on average 20 mm laterally, 7 mm superiorly and 21 mm anteriorly from its corresponding SSM.

This is the first study to apply an SSM to patients with Paprosky type II, III defects and DDH. The SSM successfully reconstructed the native anatomy of pathological hips and derived their native hip joint centre (Figure 1 [Fig. 1]).

Our findings show that the model can be used to successfully reconstruct the absent bony landmarks of patients with significant lysis regardless of the severity of the bony defect and distorted anatomy. SSM is an important tool to aid preoperative planning and implant design.