Biomechanical analysis of single screw fixation for slipped capital femoral epiphysis: Are more threads across the physis necessary for stability?

Vidyadhar Upasani, Shyam Kishan, Richard Oka, Andrew Mahar, Michael Rohmiller, Maya Pring, Dennis Wenger

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

PURPOSE: To evaluate single screw fixation stability, in the treatment of slipped capital femoral epiphysis, as a function of screw thread distribution across the physis. STUDY DESIGN: In vitro biomechanical study. METHODS: Thirty porcine proximal femurs were sectioned through the physeal line and stabilized with a cannulated 7.3-mm stainless steel AO screw. The distal 16 mm of each screw was threaded (5 threads). The femurs were randomized into 5 groups (1, 2, 3, 4, or 5 threads across the physis) and biomechanically tested to determine failure load (N) and stiffness (N/mm). RESULTS: Femurs with 2 or 3 threads across the physis had a significantly greater load to failure and stiffness compared with femurs with 1, 4, or 5 threads across the physis (P <0.05). CONCLUSIONS: Thread distribution across the physis seems to be important. When using screws with a 16-mm thread, greatest strength and stiffness are achieved when 40%-60% of threads engage the epiphysis, with a significant decrease when greater than 80% of threads cross the physis. Too few threads in the epiphysis as well as too few in the metaphysis both lead to decreased stability. CLINICAL RELEVANCE: This study challenges the belief that compression across the physis maximizes slipped capital femoral epiphysis fixation stability. We recommend equal distribution of threads across the physis when using 16-mm thread screws, and we postulate that screws with a greater thread length (32 mm or fully threaded) would increase fixation stability even further. Optimizing purchase may decrease the incidence of slip progression, especially as the prevalence of obesity increases in the adolescent population.

Original languageEnglish (US)
Pages (from-to)474-478
Number of pages5
JournalJournal of Pediatric Orthopaedics
Volume26
Issue number4
DOIs
StatePublished - Jul 2006
Externally publishedYes

Fingerprint

Slipped Capital Femoral Epiphyses
Femur
Epiphyses
Stainless Steel
Swine
Obesity
Incidence
Population

Keywords

  • Biomechanical analysis
  • SCFE fixation
  • Screw threads across the physis

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Surgery
  • Orthopedics and Sports Medicine

Cite this

Biomechanical analysis of single screw fixation for slipped capital femoral epiphysis : Are more threads across the physis necessary for stability? / Upasani, Vidyadhar; Kishan, Shyam; Oka, Richard; Mahar, Andrew; Rohmiller, Michael; Pring, Maya; Wenger, Dennis.

In: Journal of Pediatric Orthopaedics, Vol. 26, No. 4, 07.2006, p. 474-478.

Research output: Contribution to journalArticle

Upasani, Vidyadhar ; Kishan, Shyam ; Oka, Richard ; Mahar, Andrew ; Rohmiller, Michael ; Pring, Maya ; Wenger, Dennis. / Biomechanical analysis of single screw fixation for slipped capital femoral epiphysis : Are more threads across the physis necessary for stability?. In: Journal of Pediatric Orthopaedics. 2006 ; Vol. 26, No. 4. pp. 474-478.
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abstract = "PURPOSE: To evaluate single screw fixation stability, in the treatment of slipped capital femoral epiphysis, as a function of screw thread distribution across the physis. STUDY DESIGN: In vitro biomechanical study. METHODS: Thirty porcine proximal femurs were sectioned through the physeal line and stabilized with a cannulated 7.3-mm stainless steel AO screw. The distal 16 mm of each screw was threaded (5 threads). The femurs were randomized into 5 groups (1, 2, 3, 4, or 5 threads across the physis) and biomechanically tested to determine failure load (N) and stiffness (N/mm). RESULTS: Femurs with 2 or 3 threads across the physis had a significantly greater load to failure and stiffness compared with femurs with 1, 4, or 5 threads across the physis (P <0.05). CONCLUSIONS: Thread distribution across the physis seems to be important. When using screws with a 16-mm thread, greatest strength and stiffness are achieved when 40{\%}-60{\%} of threads engage the epiphysis, with a significant decrease when greater than 80{\%} of threads cross the physis. Too few threads in the epiphysis as well as too few in the metaphysis both lead to decreased stability. CLINICAL RELEVANCE: This study challenges the belief that compression across the physis maximizes slipped capital femoral epiphysis fixation stability. We recommend equal distribution of threads across the physis when using 16-mm thread screws, and we postulate that screws with a greater thread length (32 mm or fully threaded) would increase fixation stability even further. Optimizing purchase may decrease the incidence of slip progression, especially as the prevalence of obesity increases in the adolescent population.",
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T1 - Biomechanical analysis of single screw fixation for slipped capital femoral epiphysis

T2 - Are more threads across the physis necessary for stability?

AU - Upasani, Vidyadhar

AU - Kishan, Shyam

AU - Oka, Richard

AU - Mahar, Andrew

AU - Rohmiller, Michael

AU - Pring, Maya

AU - Wenger, Dennis

PY - 2006/7

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N2 - PURPOSE: To evaluate single screw fixation stability, in the treatment of slipped capital femoral epiphysis, as a function of screw thread distribution across the physis. STUDY DESIGN: In vitro biomechanical study. METHODS: Thirty porcine proximal femurs were sectioned through the physeal line and stabilized with a cannulated 7.3-mm stainless steel AO screw. The distal 16 mm of each screw was threaded (5 threads). The femurs were randomized into 5 groups (1, 2, 3, 4, or 5 threads across the physis) and biomechanically tested to determine failure load (N) and stiffness (N/mm). RESULTS: Femurs with 2 or 3 threads across the physis had a significantly greater load to failure and stiffness compared with femurs with 1, 4, or 5 threads across the physis (P <0.05). CONCLUSIONS: Thread distribution across the physis seems to be important. When using screws with a 16-mm thread, greatest strength and stiffness are achieved when 40%-60% of threads engage the epiphysis, with a significant decrease when greater than 80% of threads cross the physis. Too few threads in the epiphysis as well as too few in the metaphysis both lead to decreased stability. CLINICAL RELEVANCE: This study challenges the belief that compression across the physis maximizes slipped capital femoral epiphysis fixation stability. We recommend equal distribution of threads across the physis when using 16-mm thread screws, and we postulate that screws with a greater thread length (32 mm or fully threaded) would increase fixation stability even further. Optimizing purchase may decrease the incidence of slip progression, especially as the prevalence of obesity increases in the adolescent population.

AB - PURPOSE: To evaluate single screw fixation stability, in the treatment of slipped capital femoral epiphysis, as a function of screw thread distribution across the physis. STUDY DESIGN: In vitro biomechanical study. METHODS: Thirty porcine proximal femurs were sectioned through the physeal line and stabilized with a cannulated 7.3-mm stainless steel AO screw. The distal 16 mm of each screw was threaded (5 threads). The femurs were randomized into 5 groups (1, 2, 3, 4, or 5 threads across the physis) and biomechanically tested to determine failure load (N) and stiffness (N/mm). RESULTS: Femurs with 2 or 3 threads across the physis had a significantly greater load to failure and stiffness compared with femurs with 1, 4, or 5 threads across the physis (P <0.05). CONCLUSIONS: Thread distribution across the physis seems to be important. When using screws with a 16-mm thread, greatest strength and stiffness are achieved when 40%-60% of threads engage the epiphysis, with a significant decrease when greater than 80% of threads cross the physis. Too few threads in the epiphysis as well as too few in the metaphysis both lead to decreased stability. CLINICAL RELEVANCE: This study challenges the belief that compression across the physis maximizes slipped capital femoral epiphysis fixation stability. We recommend equal distribution of threads across the physis when using 16-mm thread screws, and we postulate that screws with a greater thread length (32 mm or fully threaded) would increase fixation stability even further. Optimizing purchase may decrease the incidence of slip progression, especially as the prevalence of obesity increases in the adolescent population.

KW - Biomechanical analysis

KW - SCFE fixation

KW - Screw threads across the physis

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