Radiographic Native Femoral Head Size Correlates with Acetabular Cup Size in Primary Total Hip Arthroplasty

Abstract

There is very little literature on whether a simple radiographic measurement of native femoral head size correlates with implanted acetabular cup size. We hypothesized that there would be a high correlation between the radiographically measured native femoral head and implanted acetabular component size in primary total hip arthroplasty (THA). We conducted a retrospective study of 277 consecutive patients who underwent primary THA. Patients with prior contralateral THA or a history of congenital deformity were excluded (n = 95). We used the postoperative anteroposterior (AP) pelvic view to calibrate the image using known implanted femoral head component size. We then measured the diameter of the contralateral native femoral head under the assumption that femoral heads are generally symmetrical in patients. Two of the authors performed all measurements. To determine if native femoral head size was correlated with acetabular component size we used the Pearson correlation coefficient (r). There was a high correlation between contralateral native femoral head size and acetabular component size (r = 0.86, 95% confidence interval [CI]: 0.82–0.89). The median difference in radiographically measured native femoral head size and acetabular component size was 7 mm (interquartile range [IQR] = 5–8). Our data showed a high correlation between acetabular component size and radiographically measured contralateral native femoral head size, with the difference being 7 mm. In addition to verifying the actual femoral head size with calipers during surgery, this simple radiographic measurement, which could be done on the affected or contralateral hip, may help surgeons to plan better and improve preoperative templating in primary THA.

Technical note for intraoperative determination of proper acetabular cup size in primary total hip arthroplasty

“…In general terms, the determination of the planned implant’s size can be carried out by specific overlays on standard plain X-rays, digital templating with or without the utilization of calibration to advanced imaging with EOS, computed tomography (CT), magnetic resonance imaging, and and customized guides for each patient[ 1 - 3 ]. Conventional planning is considered at least as robust as digital planning; however, contemporary literature is still contentious[ 5 ]. Anteroposterior pelvic radiographs are customarily used in preoperative THA templating.…”

“…Previous experience augments preoperative templating performance, as clinicians accomplish proficiency in planning the acetabular cup size after 50-100 attempts when a succinct algorithm and immediate feedback are provided[ 3 ]. A direct correlation between radiographically measured native femoral head size and implanted acetabular shell size, has been conjugated in primary THA[ 5 ]. In accordance with the literature, preoperative planning of acetabular component size features a high level of accuracy, predicting the definite implant within ± one size in 80% to 100% of cases[ 11 - 12 , 17 - 19 ].…”

“…In accordance with the literature, preoperative planning of acetabular component size features a high level of accuracy, predicting the definite implant within ± one size in 80% to 100% of cases[ 11 - 12 , 17 - 19 ]. A retrospective study of 277 patients undergoing primary THA by Pfeufer et al [ 5 ] revealed a relation between the acetabular component’s size and radiographically measured contralateral native femoral head’s size, with a discrepancy of 7 mm. Moreover, digital radiographs’ templating accuracy in predicting the implant size has been gauged and found to be sufficiently good[ 8 , 9 ].…”