Pipkin fractures: epidemiology and outcome

The National Swedish Fracture Register (SFR) was used to identify patients aged ≥ 18 years with a registered Pipkin fracture sustained in Sweden between December 1, 2013 and June 30, 2020. The SFR started in 2011 in one department, and since then a step-wise introduction of the SFR in Sweden has led to an increased coverage and completeness over the study period. At the end of 2019 the coverage of the SFR was > 90% of the 54 orthopaedic departments in Sweden [11], and full national coverage was reached in January 2021. Completeness of hip fracture registrations compared with the National Patient Register was > 80% for hip fractures for half of the active units [11], using a process described by Bergdahl et al. [12]. In the SFR, detailed data on patient, injury and fracture characteristics as well as fracture treatment is registered prospectively at each affiliated department. The energy-level (high or low) of the injury is left to the discretion of the registering surgeon to decide in the SFR. Furthermore, the SFR is linked to the national Tax Agency, from which data on patient mortality is obtained. After retrieval of the dataset from the SFR, the local hospital for each patient was contacted to gain access to individual patient records including pre- and postoperative radiographs. Preoperative computer tomography (CT) images were used to classify the Pipkin fractures as; Type 1—inferior of the fovea, Type 2—superior of the fovea, Type 3—Type 1 or 2 with concomitant femoral neck fracture or Type 4—Type 1 or 2 with concomitant acetabular fracture [7]. The classification was done by the two authors together and a consensus was reached for each case. Primary treatment was divided into non-surgical (including closed reduction), surgery with only excision of the fragment/fragments, surgery with internal fixation of the fragment/fragments using screws or bioabsorbable nails/screws, surgery with arthroplasty or other open surgical method. Closed reduction of a dislocated hip joint prior to other intervention was not recorded specifically.

To find cases who had had a secondary operation with an arthroplasty, cross-referencing was performed with the National Swedish Hip Arthroplasty Register (SHAR). The SHAR started in 1979 and collects detailed data on all primary and secondary hip arthroplasties performed in Sweden in patients with a valid Swedish personal identification number. The completeness in SHAR of primary total hip arthroplasty procedures has been > 98% over the last 10 years compared with the NPR [13].

All patients were followed until June 30, 2021, or secondary surgery with arthroplasty, or death.

With respect to the composition of the cohort, results were expressed as numbers, proportions or median (range). The Mann–Whitney U test was used for comparisons of variables in independent groups. All tests were two-sided. The results were considered significant at p < 0.05. The statistical software used was IBM SPSS Statistics, version 28 for Windows (SPSS Inc., Chicago, Illinois).

Initially, 73 patients with a preliminary Pipkin fracture were identified in the SFR. After going through the patient files and radiographs, 26 of those were found not having a true Pipkin fracture, leaving a total of 47 patients who were included in the study. The median age of the patients was 48 (18–83) years and 12 (26%) were females. The most common injury mechanism was a fall (n = 19, 40%) followed by a traffic related injury (n = 17, 36%), other injury mechanisms (n = 7, 15%) or unknown (n = 4, 8.5%). The injury level was classified as high-energy in 27 (57%), low-energy in 11 (23%) or unable to classify in 9 (19%) patients. The median follow-up time was 41 (0–90) months (approx. 3.5 years).

Classification of the Pipkin fracture type revealed that the most common fracture was Type 4 (n = 26, 55%) followed by Type 2 (n = 13, 28%), Type 1 (n = 7, 15%) and Type 3 (n = 1, 2.1%).

The primary treatment included; internal fixation (n = 21, 45%), arthroplasty (n = 13, 28%), excision (n = 7, 15%), non-surgical treatment (n = 4, 8.5%), open reduction only (n = 1, 2.1%) and autologous transplantation with fixation using graft from another part of the same femoral head (n = 1, 2.1%). All patients primary treated with arthroplasty had a total hip arthroplasty (THA) with either cemented (n = 6) or uncemented (n = 7) fixation (Figs. 1a–c, 2a–c).

The median time from injury to primary surgical treatment (43 patients) was 3.0 (0–14) days. There was no difference in the median time to primary surgical treatment between patients treated with an arthroplasty (n = 13) (3.0, 1–12 days) compared to other surgical methods (n = 30) (3.0, 0–14 days) (p = 0.8). Patients treated with primary arthroplasty were older (median 64, 51–83 years) compared to other primary surgical methods (41, 18–71 years) (p < 0.001). One patient treated with primary arthroplasty was further revised after 6 months due to dislocations, and 1 patient was revised after 2 weeks due to deep infection.

Detailed information on patient/injury characteristics and primary treatment in relation to fracture type is presented in Table 1.

The revision rate with arthroplasty among patients not treated with a primary arthroplasty was 8.8% (n = 3/34). The secondary arthroplasties were performed between 7 months and 5 years and 3 months after the injury. None of these patients were further revised due to problems with the arthroplasty. Detailed information on patients operated with a secondary arthroplasty is presented in Table 2.

A major strength of the current study was the data set including an unselected patient population from a national register—the SFR. With the Swedish personal identification number, accurate follow-up including mortality up to 1 year could be achieved. Also, joint preservation could be accurately followed by contacting each treating hospital in combination with cross-referencing with the SHAR that has excellent long-term completeness on arthroplasty procedures. Additionally, in comparison, this cohort was also one of the largest published series. Limitations includes lack of additional detailed data for each patient due to being a register study, and its retrospective design. Ideally, one would like to have had information on co-morbidity and functional status for each patient, collected prospectively.

In summary, our interpretation from the previous literature and the results from this study is that joint preserving surgery should be performed in younger patients whilst older patients can be successfully treated with a primary arthroplasty.