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Split type of greater tuberosity fracture has variety of surgical treatment options. This study aimed to compare the biomechanics property of additional cuff suture and other fracture fixation techniques.
Fifteen porcine humeri were categorized into three groups of fixation techniques those were proximal humeral internal locking system (PHILOS) plate with 2 cuff sutures, nonlocking (conventional, 3.5 mm) T-plate with 2 cuff sutures and T-plate with washer that had additional cuff suture (novel technique). Fracture was created by greater tuberosity osteotomy with 50˚ inclination to the line of surgical neck and then fixed with different prescribed techniques. Displacement of fracture site was measured with universal testing machine. The maximum forces to produce 3 mm, 5 mm of displacement and load to failure were recorded.
The average loads to reach 3 mm, 5 mm displacement and failure were 30.8 N, 45.4 N and 161 N for nonlocking T-plate; 76.6 N, 99.2 N and 144 N for PHILOS plate; 95.8 N, 120 N and 197 N for novel technique. The differences among three groups were significant in load to displacement at 3 and 5 mm (but not significant in load to failure). For load to reach 3- and 5-mm displacement, PHILOS plate and novel technique were significantly stronger than nonlocking T-plate (P < 0.05). For load to reach 3 and 5 mm displacement, novel technique was stronger than PHILOS plate but not significant (P > 0.05). For load to failure, novel technique was stronger than nonlocking plate and PHILOS plate but not significant (P < 0.05).
The important factors affecting the strength of fracture fixation are type of plate and numbers of suture augmentation that tie to the plate. Fixation with additional cuff suture showed the superior biomechanics of load to reach 3 mm, 5 mm displacement with better load to failure compared with PHILOS plate and conventional T-plate alone.
The incidence of greater tuberosity is 14 – 20 % of all proximal humeral fracture. It is usually found in young patients with high-energy trauma and in elderly or osteoporotic patients with low-energy trauma [
]. There are many techniques of fixation for split type greater tuberosity fracture, but still there has been no gold standard of treatment. Current literature showed worse function when displacement of greater tuberosity was more than 5 mm in normal population and more than 3 mm in patients involved with overhead activities [
] . But there was not any technique that used the nonlocking plate to fix this type of fracture.
Previous biomechanical studies evaluated fixation for this type of fracture and the results showed that the locking plate provided the strongest fixation strength compared to screw, single row or double row trans-osseous suture and tension band technique [
]. The disadvantage of locking plate was it had higher cost than nonlocking plate about 20 folds. So fixation with nonlocking plate is the alternative option. However, it is still lack of biomechanics evidence for using nonlocking plate in greater tuberosity fracture fixation.
The goal of this study is to compare the biomechanics between locking plate (PHILOS plate, Depuy-Synthes, MA, USA) and nonlocking T-plate. The hypothesis was no difference in the strength between nonlocking T-plate and PHILOS plate. The main outcomes were a maximum force to produce 3 and 5 mm fragment displacement and the secondary outcome was a load to failure.
Materials and methods
Fifteen porcine shoulders were harvested with age between 5 and 6 months. The experiment was carried out within 1 week of the animal's sacrifice. Porcine cadavers were classified into 3 groups of fixations: locking plate (PHILOS plate), nonlocking plate (T-plate), and nonlocking T-plate with additional suture augmentation and washer (novel technique). In term of the length of plate, we chose PHILOS plate similar to nonlocking T-plate. The step for specimen preparation were as follow. All rotator cuff muscles except supraspinatus was removed. The horizontal line was drawn from the surgical neck and the osteotomy of greater tuberosity was made from inferolateral to superomedial direction with 50˚ inclination to the line of surgical neck, as described in previous study by Gaudelli et al. [
Regarding to the fixation method in each group, all procedures were performed by one orthopaedic surgeon who had experienced for fracture fixation and suture fixation methods for more than 5 years (N.S.). All fractures were reduced anatomically and then provisionally fixed with k-wire before plate positioning. All plates were pre-contoured to align with the shape of proximal humerus and applied at about 1 cm below to the tip of greater tuberosity. Then, three 3.5-mm cortical screws (for non-locking plate) or three 3.5-mm locking screws (for PHILOS plate) were inserted at the humeral shaft distal to the fracture site in all specimens. In all group, the supraspinatus tendon was sutured at 1 cm above the greater tuberosity with two of no.2 Orthocord sutures (Depuy-Synthes, MA, USA), using modified Mason-Allen technique with 1-cm gap between each stitch. The two tails of each suture were passed through the most upper holes of the plate in the same configuration, and tied together with five surgical knots. For the novel technique group, one additional Orthocord (Depuy-Synthes, MA, USA) was sutured at 1 cm above and middle of the previous two regular stitches. Then two tails of this additional stitch were retrieved passing through two middle upper screw holes of the plate, looped around the the head of most top of screw and underneath the washer, and tied with surgical knot as shown in Fig. 2.
The humeral shaft of specimens was fixed to a mounted testing unit (Universal testing machine) and supraspinatus muscle was sutured with 2 high strength sutures (No.5 Ethibond, Ethicon, Belgium) and wire in Krackow suture. Four tails of high strength suture and 2 tails of wire were connected to the base of the mounted testing unit.
Marking screws were fixed at the proximal humerus and the osteotomized greater tuberosity fragment. Displacement of fracture site was collected by measuring the gap between the marking screws after applied the load with dial gauge (ABSOLUTE Digimatic Indicator ID-C (model 543-404B) (Mitutoyo Corporation, Japan).
The load was applied along the supraspinatus tendon perpendicular to the longitudinal axis of the humeral shaft as shown in Fig. 3. The maximum forces those made 3 mm, 5 mm and load to failure of greater tuberosity displacement were recorded. The definition of failure was the muscle or tendon tear due to suture cut-out.
Stata version 15 was used for statistical analysis. One-way ANOVA test was performed for comparing between 3 groups. Comparison within each experimental group was used with Scheffé test. Significant level was set at P ≤ 0.05.
Different (P<0.05) from factor nr
Load to 3 mm displacement ANOVA Scheffé test for all pairwise comparisons
Comparing in each group by using Scheffé test, nonlocking T-plate demonstrates the average load to reach 3 mm of displacement less than PHILOS plate and novel technique significantly (p = 0.001). Novel technique uses the load to reach 3 mm of displacement more than PHILOS plate but not significant (p > 0.05).
Regards the load to reach 5 mm of displacement, nonlocking T-plate group reveals the average load less than PHILOS plate group and novel technique group significantly (p < 0.001). However, the average load to reach 5 mm of displacement in novel groups is comparable to those in PHILOS plate group (p > 0.05).
For the load to failure, novel technique group shows the average load to failure more than both nonlocking T-plate and PHILOS plate groups, but not significant (p = 0.077).
Multiple surgical techniques have been described in the literature such as transosseous suture, screw fixation, tension band, anchor suture, locking plate fixation. Screw fixation method is a simple and effective procedure, but it may break the fragment of greater tuberosity especially in comminuted fracture. The comminuted fracture of greater tuberosity generally prefers to use the anchor suture or plate and screw fixation because these techniques can stabilize the greater tuberosity by suturing the rotator cuff and stabilize the fragments with single row or double row technique by anchor suture fixation or tying the knot to the plate's hole.
From previous biomechanical studies, Braunstein et al. reported the strength of various fixations, including transosseous suture, screw fixation and tension band wiring. The result showed that tension band wiring is stronger than screw fixation and transosseous suture, respectively [
]. Brais et al. performed a study comparing the strength among tension band suture, double-row fixation and transosseous braided-tape in porcine proximal humerus. Double-row fixation and transosseous braided-tape had similar mechanical properties and were stronger and more stable than tension band suture [
]. Seppel et al. performed a study in human cadaveric shoulder that compared the strength of fixation between single-row and double-row by using suture tape. The result showed no different in strength of both technique [
]. Another biomechanical study compared the strength among tension band, double row and locking plate. The result showed that the locking plate had higher mean load to produce 3 mm and 5 mm displacement than double row and tension band, respectively [
]. So, we may imply that locking plate fixation is the strongest implant for treatment in isolated greater tuberosity fracture. But the main drawback of locking plate fixation is high cost. In term of cost effectiveness, the use of nonlocking plate seems to be a better choice than locking plate. For example, in Thailand the cost of nonlocking T-plate is about 980 baht (27.2 USD) compared with 19,700 baht (547.2 USD) for PHILOS plate. The difference in cost is about 20 times and it can be saved approximately 18,720 baht (520 USD) per fixation by using nonlocking T-plate. Other advantages of nonlocking T-plate are low profile and easy to contour which reduces soft tissue irritation. From our knowledge, the intact rotator cuff acts as deforming force to the greater tuberosity fragment. Therefore, the use of suture to place around tendon-bone junction and tie to plate's holes is the main stabilizer of greater tuberosity fragment. The result of this study showed that our novel technique provided the strength as same as PHILOS plate and better than the standard nonlocking T-plate. We hypothesized that the compression of fracture site could occur by 2 ways in this combined tension suture and plate fixation. First, the fracture could be compressed from the precontour plate during screw insertion on the humeral shaft. Second, the tension suture that are passing over the greater tuberosity to the screw holes would result in some compression of fracture site as same as the standard suture anchors fixation shown in previous study by Lin et al [
]. Moreover, the stiffness of tension suture construct should be mainly depended on the suture fixation characteristics such as the number and the size of suture, the suture materials and the suturing surgical techniques. This is because the suture would act as the tension band to withstand the physiologic load of greater tuberosity. The fixation only on the diaphysis segment is designed to use plate as a suture post which should be strong enough to withstand the physiological load on the greater tuberosity fragment.
According to technique of fixation in the study, the novel technique is almost the same as nonlocking T-plate except for the additional suture augmentation and washer. However, it provided the same strength as PHILOS plate. It can assume that type of plate is not a main factor that has influence on the strength of fixation. However, another important factor for the strength of fixation is the number of suture augmentation. In aspect of the cost, T-plate is as same as novel technique and less than PHILOS plate. According to the cost, novel technique is the alternative option for split-type greater tuberosity fracture fixation because it provides the same strength but lower cost than PHILOS plate.
Limitation of this study is the use of porcine shoulder due to the difficulty to find the intact human shoulder cadaveric specimens. Bone quality of pig specimen is very good which represents young humeri. It should be careful to apply the result in an elderly patient with osteoporotic bone. However, the incidence of greater tuberosity fracture tends to occur in young patient [
]. Thus, it is reasonable to use porcine cadaveric model. Another limitation is porcine shoulder anatomy is different from human, but the concept of fixation is still the same. The main stabilizer is the suture that pass rotator cuff and tie to plate's hole. Thus in this study, no screw is inserted into the greater tuberosity fragment.
Factors those affect the strength of fixation is type of the plate and number of suture augmentation. The recommended alternative technique for split-type greater tuberosity fracture fixation is additional cuff suture (novel technique) that using T-plate with 3 sutures augmentation. This study proved that novel technique of fixation had mechanical advantage and worth to choose for split-type greater tuberosity of humerus fracture.
Declaration of Competing Interest
All authors do not have any financial and personal relationships with other people or organizations that could inappropriately influence this article.
The authors wish to thank Department of Orthopaedics, Faculty of Medicine Ramathibodi Hospital, Mahidol University for the kind assistance and permission to carry out this study. We also deeply appreciate the support from Dr. Panya Aroonjarattham from the Department of Mechanical Engineering, Faculty of Engineering, Mahidol University for the fabulous biomechnics labolatory.