The effectiveness of a single 6.5 or seven-millimeter diameter screw for the promotion of premature physeal closure and the provision of stability of a slipped capital femoral epiphysis was investigated. Physeal fusion was demonstrated in forty-nine (92 per cent) offlfty-three hips after fixation with a single screw. Premature fusion ofthe involved physis, compared with the uninvolved, contralateral physis, was documented (p < 0.001). Epiphyseal stability, as measured by the lateral head shaft angle, was maintained in all except one hip. An analysis of twenty-nine hips for which there was a complete set of radiographs, that were in patients who had no endocrine problems, and that were the first hips entered into the study when the patient had bilateral involvement, revealed an average time to closure of the physeal line of thirteen months. A longer time to physeal fusion was correlated with increasingly eccentric placement of the screw (r = 0.44, p = 0.016) and increasing severity of the slip (r = -0.536, p = 0.003). There was no correlation between the age at the time of the operation, race, or sex and the time to physeal fusion. Only one patient had penetration by a screw, and no chondrolysis, avascular necrosis, or other serious *No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study. tChildren’s Hospital of Pittsburgh, 3705 Fifth Avenue, Pittsburgh, Pennsylvania 15213. Please address requests for reprints to Dr. Timothy Ward. tUniversity of Minnesota Medical Center, 420 Delaware Street. SE., Minneapolis, Minnesota 55414. §Children’s Hospital of Michigan, 3901 Beaubien Boulevard, Detroit, Michigan 48201. problems developed. Fixation with a single 6.5 or sevenmillimeter-diameter screw provided adequate epiphyseal stability and promoted premature physeal fusion in our patients, while decreasing the rate of complications compared with that reported to be associated with fixation with multiple screws or pins. Fixation with multiple pins or screws has been widely accepted as treatment for either acute or chronic slipped capital femoral epiphysis. The advantages of fixation with multiple pins include a shortened operative time and diminished loss of blood compared with the more extensive procedures of open bone-grafting or osteotomy’732 ’. The objectives of treatment with multiple pins or screws are the prevention of further slipping of the epiphysis and the promotion of premature fusion of the physis. However, since Walters and Simon3 first called attention to the problem of unrecognized penetration by pins, a disturbingly high prevalence of both recognized and unrecognized penetration by pins has been reported24754252t’25. Some authors have reported penetration by pins and clustering of pins to be factors in the subsequent development of chondrolysis and avascular necrosis325; others have found no such association27. Stambough et al.25, Ordeberg et al.2’, and Bennet et al.2 reported that the over-all rate of complications after fixation with pins or screws for the treatment of slipped capital femoral epiphysis is directly related to the number of pins or screws inserted. The use of a single screw for fixation of a slipped epiphysis should decrease the prevalence of penetration by screws and the volume of the femoral head that is occupied by metal. If the goals of epiphyseal stabilization and premature closure of the

Fixation with a single screw for slipped capital femoral epiphysis.

Slipped capital femoral epiphysis (SCFE) is a common hip condition that can be disabling. In this review, we provide an orientation on current trends in the clinical management of SCFE including conventional procedures and specialised surgical developments. Different methods of fixation of the epiphysis, risks of complications, and the rationale of addressing deformity, primarily or secondarily, are presented. Although improved understanding of the anatomy, vascularity and implications of residual deformity have changed management strategies, the best modality of treatment that would restore complete vascularity to the femoral head and prevent any residual deformity, impingement and early osteoarthritis remains elusive.

Current concepts in management of slipped capital femoral epiphysis.

There is an ongoing debate on which fixation technique should be preferred for the prophylactic fixation of the asymptomatic contralateral hip in slipped capital femoral epiphysis (SCFE). In the case of Kirschner-wire (K-wire) fixation, there is a possibility of secondary loss of fixation because of longitudinal growth of the physis, whereas in screw fixation, physeal growth of the femoral neck might be impaired. The aim of this matched-pair study was to compare the longitudinal growth of the femoral neck in screw fixation versus K-wire fixation of the asymptomatic contralateral hip in SCFE. All 18 patients (female:male=3:15), who had undergone screw fixation of the asymptomatic contralateral hip between 9/2001 and 9/2011, were matched according to age, bone age, sex, and time to follow-up to another 18 patients with K-wire fixation. The length of the femoral neck of the contralateral hip was measured in parallel to either screw or K-wire from the apex of the femoral head to the opposite cortical bone. The ratio of the femoral neck length measured directly after surgery and on follow-up was defined as femoral neck growth. There was no significant difference between groups with respect to age, modified Oxford Bone age score, and time to follow-up. We found a significant difference in femoral neck growth between patients with screw fixation (5.5 ± 4.3%) compared with K-wire fixation (8.9 ± 5.7%, P = 0.048 matched Wilcoxon test). The difference in femoral neck growth of patients with K-wire or screw fixation of the contralateral asymptomatic hip in SCFE was small, but statistically significant. Thus, despite high rates of secondary loss of fixation, K-wire fixation should still be considered, especially in very young patients.

Significantly lower femoral neck growth in screw fixation of the asymptomatic contralateral hip in unilateral slipped capital femoral epiphysis

Time-elapsed screw insertion with microCT imaging.

Hintergrund: Fur eine gering- bis masiggradige Epiphyseolysis capitis
 femoris (ECF) stellt die operative In-situ-Fixation den aktuellen
 Behandlungsstandard dar. Hinsichtlich der Art der operativen Versorgung
 gerade in Hinblick auf Schrauben- vs. Drahtversorgungen sowie der
 prophylaktischen Versorgungen der gesunden Hufte gibt es weiterhin
 Uneinigkeit. Ziel dieser Studie war die Analyse eines femoralen
 Restwachstums sowie femoraler Deformitaten nach In-situ-Fixation der ECF
 mittels Kirschner-Drahten und Kurzgewindeschrauben. Patienten und
 Methoden: Es erfolgte eine retrospektive radiologische Analyse aller
 zwischen 01/2003 und 02/2011 operativ versorgten Patienten mit ECF. Zur
 Evaluation des femoralen Wachstums wurden die artikulotrochantare Distanz,
 zentrotrochantare Distanz, Centrum-Collum-Diaphysen-Winkel (CCD-Winkel),
 Pin–joint Ratio und Pin–physis Ratio bestimmt. Die femorale Deformitat wurde
 uber die Ermittlung der Spharizitat ermittelt. Zur Analyse der azetabularen
 Beteiligung wurden der CE- sowie der ACM-Winkel gemessen. Degenerative
 Veranderungen wurden im Abschlussrontgenbild erfasst. Die Ergebnisse der
 therapeutisch versorgten Huften wurden den prophylaktisch versorgten
 gegenubergestellt und Draht- bzw. Schraubenversorgungen wurden miteinander
 verglichen. Ergebnisse: Insgesamt wurden 22 Patienten
 (w : m = 14 : 8, Durchschnittsalter Madchen: 11 ± 1 Jahre, Jungen: 13 ± 2
 Jahre) mit 26 Epiphyseolysen analysiert. Kirschner-Draht-Spickungen
 erfolgten in 4 Huften therapeutisch, in 4 Huften prophylaktisch und
 Verschraubungen in 22 Huften therapeutisch sowie in 14 Huften
 prophylaktisch. Es zeigte sich kein signifikant fruherer
 Wachstumsfugenverschluss fur die Schraubenfixationen. Hinsichtlich der
 femoralen Wachstumsparameter ergab sich insgesamt eine signifikante Abnahme
 der artikulotrochantaren Distanz sowie des CCD-Winkels. Die Pin–joint Ratio
 ergab in 58 % der therapeutisch und in 72 % der prophylaktisch versorgten
 Huften ein adaquates Wachstum, wobei kein Unterschied zwischen
 Kirschner-Draht- und Schraubenversorgungen bestand. Auch die Pin–physis
 Ratio zeigte vergleichbare Werte. Hinsichtlich der femoralen
 Deformitatsparameter ergab sich fur die therapeutisch versorgten Huften eine
 deutlich schlechtere Spharizitat, die im Verlauf unverandert blieb. Durch
 die prophylaktische operative Versorgung ergab sich keine Verschlechterung
 der Spharizitat. Die azetabularen Wachstumsfaktoren zeigten keine
 signifikanten Veranderungen. Schlussfolgerung: Die Ergebnisse lassen
 auf ein weiteres Wachstum des proximalen Femurs nach dem Einbringen einer
 Gleitschraube zur In-situ-Stabilisierung von mild bis moderaten
 Huftkopfepiphysenlosungen schliesen, ohne dass bis zum Wachstumsabschluss
 eine Zunahme der Deformitat auftritt. Ihre Berucksichtigung scheint sowohl
 als Entscheidungshilfe zur Implantatwahl als fur die Indikationsstellung zur
 prophylaktischen Versorgung der nicht betroffenen Seite wertvoll.

Wachstum und Deformität nach In-situ-Fixation der Epiphyseolysis capitis femoris

INTRODUCTION Previous data have shown that due to the technical ease, low-morbidity, and lower complication rates, the in situ single-implant fixation is the current standard for stabilization of slipped capital femoral epiphysis (SCFE) fixation. Multiple-implant fixation is thought to be combined with a higher incidence of serious complications. The purpose of the current study was to evaluate single- vs. multiple-implant fixation regarding strength and stiffness. Furthermore, different screw designs, including telescopic screw, were evaluated regarding the stiffness, strength, and especially fixation failure. METHODS Forty porcine proximal femurs were sectioned through the physeal line using a gigli saw and stabilized with a 7.3-mm stainless steel AO screw, a dynamic telescopic screw, three 1.6-mm Kirschner wires (K-wires), and three 2.0-mm K-wires. The femurs were biomechanically tested to determine failure load (N) and stiffness (N/mm). RESULTS No significant differences were found regarding failure load and stiffness between the two screw groups. The 2.0-mm K-wire construct was significantly the strongest and stiffest fixation. The 1.6-mm K-wire fixation had the lowest values, but not statistically significant. Regarding the fixation failure, no femoral shaft fracture occurred. CONCLUSION SCFE stabilization with three 2.0-mm K-wires leads to increased stability over single-screw fixation and 1.6-mm K-wire fixation. However, none of the two screws seemed to be superior in fixation stability and fixation failure.

Biomechanical analysis of screw fixation vs. K-wire fixation of a slipped capital femoral epiphysis model.

Local interpretation of micro finite element (μFE) simulations has become important in different fields of bone biomechanics. Although on an apparent level μFE has successfully been validated against experiments, local validations are sparse and limited by imaging resolution. At the tissue level heterogeneity of Young’s modulus has been reported. Although non-uniform material distribution have been shown to only have a minor influence on the apparent material properties, its impact on local material behaviour is largely unknown. By combining image-guided failure assessment (IGFA) using synchrotron-based-micro-computed tomography, strain mapping and inverse μFE modelling, we present an experimental and computational framework which will allow studying local effects of intratrabecular heterogeneity of the Young’s modulus.

/pdf/image-guided-failure-assessment-of-human-trabecular-bone-418tons7mx.pdf

Image-guided failure assessment of human trabecular bone - Inverse finite element modelling for characterization of elastic properties.

Angular stable implants reduced the complication rate in the treatment of humeral head fractures. But the failure rate is still high. To further reduce the risk of cut-out, cement augmentation of screws was introduced. A reason for failure of plate osteosynthesis might be the extremely high stiffness of the screw-plate interface leading to a loss of reduction and cut-out of screws. A more homogeneous distribution of the forces on all screws may avoid secondary dislocation. We hypothesize that dynamic osteosynthesis minimizes screw loosening and results in a higher load to failure than standard locking screws. Twelve paired human humerus specimens were analysed. A standardized three-part fracture model with a metaphyseal defect was simulated. Within each pair of humeri, one was fixed with a Philos plate and standard locking screws (LS), whereas the other humerus was fixed with a Philos plate and dynamic locking screws (DLS). A cyclic varus-bending test or a rotation test with increasing loading force was performed until failure of the screw-bone-fixation. In the varus bending test, pairs failed by screw loosening in the humeral head. The LS-group reached 2901 (601–5201) load cycles until failure, while the DLS-group failed after 3731 (2001–5601) cycles. This corresponds to a median loading of 195 N for the LS-group and 235 N for the DLS-group (p = 0.028). In the rotation test the LS-group reached a median of 1101 (501–1501) load cycles until failure of fixation occurred, while the DLS-group failed after 1401 (401–2201) cycles (p = 0.225). Plate fixation using dynamic locking screws for the treatment of proximal humerus fractures demonstrated more load cycles until failure compared to standard locking plate osteosynthesis.

/pdf/dynamic-locking-screws-in-proximal-humeral-plate-56npw4opny.pdf

Dynamic locking screws in proximal humeral plate osteosynthesis demonstrate superior fixation properties: a biomechanical study

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Papers

Biomechanical analysis of screw fixation vs. K-wire fixation of a slipped capital femoral epiphysis model.

Image-guided failure assessment of human trabecular bone - Inverse finite element modelling for characterization of elastic properties.

Dynamic locking screws in proximal humeral plate osteosynthesis demonstrate superior fixation properties: a biomechanical study