BACKGROUND Fibular deficiency is a common long-bone deficiency with an estimated incidence of 7.4-20 cases per million live births. Absence or hypoplasia of the cruciate ligaments is present in most patients with fibular deficiency. In one series, the anterior cruciate ligament (ACL) was deficient in 95% while the posterior cruciate ligament (PCL) was deficient in 60% of patients with fibular deficiency. Symptomatic instability of the knee is variably present in patients with congenital absence of the ACL including fibular deficiency, with a reported incidence of between 3% and 50%. Despite this reported incidence, limited literature assessing the perceived knee stability in patients with fibular deficiency exists. METHODS Patients diagnosed with fibular hemimelia with congenital absence of the ACL were identified retrospectively at a pediatric hospital. Of the identified patients over the age of 16, 28 agreed to be part of the study and were sent an online survey. They completed Lysholm and Patient-Reported Outcomes Measurement Information System (PROMIS) surveys on knee problems, physical function, pain intensity, and overall health. The PROMIS raw score responses were converted to a T-score, scaled to a mean of 50 points (representative of the mean of the reference population), with a standard deviation of 10 points. Any response more than one standard deviation away from 50 was considered worthy of further review. 18 patients returned surveys, and these individuals comprise the final study group. RESULTS Of the study patients, the average age was 19.8 years (16-24 years), with 7 females and 11 males. 9 patients are amputees and 9 are non-amputees. On the Lysholm Knee Scoring Scale, the highest possible score is 100 points, which relates to normal knee function. Our average Lysholm score was 79.94, with a wide range in scores from 25-100 points, in comparison to the average adult knee score of 94 (Briggs et al). The amputee average Lysholm score was 77.8 and the non-amputee average Lysholm score was 74.1, with no statistically significant difference. For our cohort, the mean Physical Function T-score was 52 (range 27.5-60.1), with a higher score relating to better physical function. The amputee average score was 53.1 and the non-amputee average score was 45.8, with no statistically significant difference. 12 respondents reported normal physical function compared to the general population, with 8 more than 1 standard deviation (SD) above a T-score of 50. Of the 6 respondents with a physical function score lower than 50, 4 reported mild functional impairment (.5 – 1.0 SD), 1 moderate impairment (1.6 SD), and 1 severe impairment (2.25 SD). The severe impairment was reported by an amputee and the moderate physical impairment reported by a non-amputee. For the PROMIS Global Physical Health domain, the mean T-score was 52.6 (range 29 -63.3). There was no significant difference between the average scores of the amputee (54.8) and non-amputee (50.3) groups. 13 respondents had no difference or had better health than the normal population mean, with 8 being amputees and 5 being non-amputees. 5 respondents had the highest possible score of 63.3, which is 1.33 standard deviations better than the normal average (2 non-amputees and 3 amputees). Of the 5 patients (4 non-amputees and 1 amputee) reporting worse health, only 1 respondent reported severe health impairments (2.1 SD). All PROMIS subject areas measure whether more of the domain occurs. For Physical Function and Global Health, a higher score indicates improved function. In the Pain Intensity realm, a higher score relates to more pain. In this study population, the mean pain T-score was 40.15 (range 30.7 – 60.5). The amputee average score was 38.98 and the non-amputee average score was 41.3, with no significant difference between them. 16 patients had less pain or normal pain levels compared to the population mean. Of the two patients reporting worse pain than the normal population, the amputee patient had mild pain (within 1 SD of 50) and the non-amputee had moderate pain (1.05 SD). CONCLUSIONS The only previously published report on knee function in adults with fibular deficiency contained 11 patients; our 18 patients substantially expands data available on knee function in these patients. Previously, Crawford, et al, obtained Lysholm and Musculoskeletal Outcomes Data Evaluation and Management System (MODEMS) scores on nine patients treated since 1928. Their data demonstrated an average Lysholm score of 90.2, compared to ours of 79.94. The majority of our patients demonstrated excellent PROMIS responses, with 12-15 demonstrating average or above pain, physical function, and global health scores. Amputees tended to self-report better health than the non-amputees. Overall, in the young adult cohort, we demonstrate that the majority of patients with fibular deficiency function well and have a stable knee, although a small subset of patients do have challenges with knee function.
APPENDIX I: COEFFICIENTS (
a
i
AND
b
i
) OF THE BEST ESTIMATES OF THE MEAN (
μ
) AND STANDARD DEVIATION (
σ
) IN CENSORED SAMPLES UP TO
n
= 20 FROM A NORMAL POPULATION
