• Basic Science

A novel osteosynthesis method, the Composite Patch Technique (CPT), has been proposed as a potential alternative to conventional metal plate fixation. The CPT is an in situ customizable technique that employs a composite applied directly over the fracture, anchored with conventional screws, and cured using high- energy visible (HEV) light. At present, the CPT is a prototype not tailored to any specific fracture type. Prior to this PhD project, only one study had been published on the CPT, highlighting its potential benefits in managing complex fractures due to its customizability and a possible advantage in phalanx fractures by potentially reducing tendon adhesions. Building on these preliminary findings, the objective of this thesis was to investigate the biomechanical performance and clinical applicability of the CPT in relation to phalanx fracture management and as a general osteosynthesis technique.
Study I compared the biomechanical performance of the CPT to a stainless-steel locking plate (LP) in an ex vivo ovine proximal phalanx fracture model using 4-point bending and torsion tests in both a reduced and a 3 mm gap model. The CPT demonstrated significantly lower maximum bending moment (BM) and torque in both fracture models, and lower bending stiffness (BS) in the gap model. Conversely, the CPT exhibited higher BS in the reduced model and greater torsional stiffness (TS) compared to LP. In conclusion, there were differences in biomechanical performance between the CPT and the LP. However, higher BS in the reduced model and greater TS suggest that the CPT might offer sufficient stability in selected phalanx fracture cases, while its application is likely limited in more complex or unstable fractures.
Study II evaluated the usability of the CPT by assessing inter- and intra-surgeon biomechanical variability in maximum BM and BS, in a synthetic small tubular bone fracture model in 4-point bending. Six surgeons with varying levels of experience (one surgeon with CPT experience) each performed 9–10 consecutive osteosyntheses (n = 59) after reviewing an instruction manual and completing one supervised application. One surgeon demonstrated increased maximum BM, and another showed improved BS across trials. Significant variability was observed between surgeons in both parameters. In conclusion, these findings suggest that CPT can be learned and applied with limited training. However, the observed inter-surgeon variability indicates limited biomechanical standardization, and the clinical significance of this remains uncertain.
Study III was conducted in two parts using a human ex vivo proximal phalanx midshaft fracture model. Part I quantified the internal BM occurring across a 3 mm gap fracture during simulated fingertip-to-palm (FTP) motions. Part II evaluated the performance of the CPT during three consecutive FTP-motions (outcome: visual
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inspection) and assessed load tolerance during motion to failure (outcome: maximum force at the fingertip recorded from a force-transducer), in both a reduced and a 3 mm gap fracture model. The internal BM during FTP-motions was 6.78 ± 1.62 Nmm. CPT constructs withstood three repeated FTP-motions without failure and ultimately failed at a mean load of 48.48 N (range: 27.4–61.1 N). In conclusion, CPT provided sufficient stability to tolerate simulated FTP-motions in this controlled setup. These findings suggest that the CPT may offer adequate stability for early mobilization in selected phalanx fractures.
Study IV was an in vivo ovine analysis comparing the stability of the CPT to a LP in a bilateral proximal midshaft-reduced phalanx fracture model. Eight sheep were included, yielding 16 samples (8 CPT and 8 LP). The primary outcome was radiographic evaluation one week post-surgery. To offload the operated phalanx, limbs were protected using either a walking cast or a custom shoe on the medial digit, and animals were allowed unrestricted movement post-surgery. All CPT constructs failed, while all LP fixations remained intact except for one case of screw loosening. In conclusion, CPT did not provide stability comparable to LP in this fracture model, indicating limited applicability in weight-bearing fractures or in fractures at risk of unpredictable loads.
The findings in this thesis indicate limited clinical applicability of the CPT in phalanx fractures and other fracture types. Despite findings of potentially sufficient stability relevant for select phalanx fractures, the failures in vivo demonstrate the many uncertainties regarding biomechanical performance in turn limiting safe conclusions on clinical applicability in fracture management. As an osteosynthesis technique, the findings indicate that its customizability allows for in-situ modifications, as demonstrated by increased torsional stability by increased width and that the CPT can be learned and applied in a controlled environment.