Tibial bowing and tibial component placement in primary total knee arthroplasty in valgus knees: Are we overlooking?

PURPOSE

Tibial bowing in valgus knees with arthritis can lead to component malplacement during total knee arthroplasty (TKA). Incidence of valgus knees with medial tibial bowing, its effect on tibial component placement during primary TKA and methods to improve accuracy of the component placement were studied.

METHODS

Full-length weight-bearing alignment radiograph was taken in 117 patients (149 knees) with valgus deformity undergoing TKA. In these cases, the proximal tibial reference for extramedullary jig placement was planned preoperatively with reference to the tibial spines and classified as four zones.

RESULTS

The mean preoperative hip-knee-ankle (HKA) angle was 192.9° (180.3-234.5°). Bowing >3° was considered significant (p < 0.001) and at this level of bowing, the proximal tibial reference was shifted from centre to medial. Tibial bowing <3° was considered straight and >3° as tibia valga. Tibia was bowed in 70 knees (46.97%). Severity of valgus deformity had strong positive correlation with the tibia valga (p < 0.001). The post-operative medial proximal tibial angle (MPTA) and HKA angle were 91.63° (87.9-95.7°) and 182.6° (178.1-189.7°), respectively. The mean MPTA and post-operative HKA angle in bowed and straight tibiae were 90.35° versus 89.78° (p = 0.547) and 181.5° versus 180.7° (p = 0.5716), respectively, and the difference was not statistically significant.

CONCLUSION

Medial tibial bowing is very common in valgus knees. Tibia valga has a strong positive correlation with the severity of valgus deformity. Accurate tibial component placement can be achieved with a medialized reference point for extramedullary tibial cutting jig in knees with significant tibia valga. The study has been registered in clinical trials registry - India (CTRI/2018/03/012283).

Increased bone turnover, osteoporosis, progressive tibial bowing, fractures, and scoliosis in a patient with a final-exon SATB2 frameshift mutation

Haploinsufficiency of SATB2 causes cleft palate, intellectual disability with deficient speech, facial and dental abnormalities, and other variable features known collectively as SATB2-associated syndrome. This phenotype was accompanied by osteoporosis, fractures, and tibial bowing in two previously reported adult patients; each possessed SATB2 mutations either predicted or demonstrated to escape nonsense-mediated decay, suggesting that the additional bone defects result from a dominant negative effect and/or age-dependent penetrance. These hypotheses remain to be confirmed, as do the specific downstream defects causing bone abnormalities. We report a SATB2 mutation (c.2018dupA; p.(H673fs)) in a 15-year-old patient whose SATB2-associated syndrome phenotype is accompanied by osteoporosis, fractures, progressive tibial bowing, and scoliosis. As this homeodomain-disrupting and predicted truncating mutation resides within the final exon of SATB2, escape from nonsense-mediated decay is likely. Thus, we provide further evidence of bone phenotypes beyond those typically associated with SATB2-associated syndrome in individuals with potential dominant-negative SATB2 alleles, as well as evidence for age-dependence of bone features. Elevations in alkaline phosphatase, urinary N-telopeptide/creatinine ratio, and osteocalcin in the patient indicate increased bone turnover. We propose surveillance and treatment with osteoclast inhibitors to prevent fractures and to slow progressive bone deformities. © 2016 Wiley Periodicals, Inc.

The use of anterolateral bowing of the lower leg in the diagnostic criteria for neurofibromatosis type 1

Neurofibromatosis type 1 is diagnosed clinically based on the presence of two of seven criteria developed by a panel of experts in 1987. The sixth criterion focuses on skeletal findings and is as follows: "A distinctive osseous lesion such as sphenoid dysplasia or thinning of long bone cortex, with or without pseudarthrosis." The wording for this criterion is misleading. In particular, "thinning of long bone cortex" is not the characteristic radiographic presentation, and no mention of long bone bowing is included. The distinctive clinical feature of long bone dysplasia in neurofibromatosis type 1 is anterolateral bowing of the lower leg (portion of the body delimited by the knee and ankle). The usual radiographic findings of long bone dysplasia in neurofibromatosis type 1 at first presentation, prior to fracture, are anterolateral bowing with medullary canal narrowing and cortical thickening at the apex of the bowing. We suggest that anterolateral bowing of the lower leg, with or without fracture or pseudarthrosis, is a more appropriate description of the primary finding that a clinician will use to fulfill the sixth diagnostic criterion for neurofibromatosis type 1. Clarification of this diagnostic criterion is important for the clinician and for research protocols. Appropriate interpretation will improve understanding of the natural history and pathophysiology of neurofibromatosis type 1.