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Design And Clinical Application Of Swan-Like Memory Connector For Humeral Shaft Nonunion

Jia-can Su*, Xin-wei Liu*, Chun-cai Zhang, Hua-peng Guan, Zhuo-dong Li, Lie-hu Cao

* Department of Orthopedic surgery, ChangHai Hospital, The Second Military Medical University, Shanghai, China.  

Address for Correspondence:  

Xin-wei Liu
Department of Orthopedic surgery, 
Changhai Hospital, 
The Second Military Medical University 
Shanghai, 200433,China.
Tel: +8621-25072003, 
Fax: +8621-25074066, 



Objective: To develop a new method of treating fractures and nonunion of humeral shaft.

Methods: A nitinol connector named swan-like memory compressive connector (SMC) was designed. The biomechanics test included photoelasticity, electrometric method and three dimensional finite element analysis were employed. In clinical application, 105 cases of nonunion of a humeral shaft fracture between 1990 to 2001 were analyzed retrospectively. Among the 95 patients, there were 56 males and 39 females with an average age of 46.2 years (range from 17 to 71 years). All the nonunions were managed by open reduction and internal fixation with SMC and cancellous bone graft. The mean follow-up period was was an average of 38 months (range from 25 to 81 months).

Results: All nonunion fractures united within an average of 16 weeks (range 10-26 weeks) and the nonunion sites were substituted by plate-like bone. At the final follow-up, shoulder and elbow functions of the operated limbs were all satisfactory.

Conclusions: The SMC provided a new method for fracture fixation and treatment of bone nonunion for upper limb diaphysis, and maybe develop a new way to prompt bone healing.

J.Orthopaedics 2008;5(2)e16

Humeral shaft; Fracture; Nonunion; internal fixation;

The incidence of nonunion after humeral shaft fractures is generally reported as low because of the favorable results of nonoperative 1 and, on strict indication, surgical treatment 2.Nonunion of the humeral shaft occurs in 2% to 10% of nonsurgically treated fractures and in up to 15% of fractures treated by primary open reduction and internal fixation (ORIF) 3-6.Despite advances in the initial management of upper limb fractures, some result in nonunion, requiring further intervention. Because the treatment of nonunion is time consuming and difficult, successful initial fracture management is important. The treatment of nonunion of a humeral shaft fractures was considered difficult by Watson-Jones7,and several operative options have been reported in recent decades 8-12, including dynamic compression plate (DCP) with cancellous bone grafting, intramedullary nailing (IM), external fixation, vascularized bone graft, and on-lay bone-plate augmentation. Different success rates and complications have been reported for these options. There are some reports of managing nonunion of a humeral shaft fracture with DCP and cancellous bone grafting. Fracture healing is related to its local stress enviroment. According to wolff’s theory, bones have functional adaptability to external load and bone structures relate to corresponding stress. Humerus don’t belong to weight-bearing bone, so how to provide the shaft an axial anti-shearing, anti-bending and anti-torsion fixation and at the same time provide stable biomechanic enviroment adaptive to anatomy and physiology at the fracture site until bone healing? In August 1990 we designed nitinol shape memory connector (I、II type), looking like a swan, and was named Swan-like Memory-pressure Connector(SMC). Untill August 2001, SMC had been used in the treatment of humeral nonunion with 105 cases and we got high union rates.

Material and Methods :

Design of SMC

An image of a wet humeral sample was formed with a constant axis by CT, the thickness of layer was 2 mm with 160 layers. The pictures were fed to the computer to form the cross section picture of each layer. Both three dimentional model establishment and finite element (FE) analysis were based on Windows XP platform and the major software for FE analysis was Simpleware2.0 (Exeter, UK). The model was described as a mesh of three-dimensional ten-node tetrahedral solid elements the whole humerus were divided into 2729 nodes including 49041 units.In this research, we presumed that the humeral material was continuous, well distributed, linearly elastic and same in all directions, the elasticity modulus was 13400 Mpa when compressed and Poisson’s ratio was 0.30.

According to the anatomic morphology and biomechanic features of humerus, we combine the material nickel (50-53%) and titanium(47-50%), 1.5 to 2.5mm in thickness, producing the SMC. This device consists three parts: swan body, swan neck (axial compression part), swan wing (holding part). (Fig. 1)The inside diameter of SMC was 6 to 23mm, inside and diameter length ratio was about 1:6. Reverting temperature was 33±2.

Fig. 1 Diagram of Swan-like Memory Connector used to treat fracture and nonunion of the humerus

An oversized working model of the initial design idea was manufactured by one of the authors (Chuncai Zhang) and the mechanism was shown to work well. However, there was much development to be undertaken to produce a design of SMC small enough and strong enough for use in the humerus of a human. (Fig.2)

Figure 2:schematic diagram of humerus fixated with SMC

We tested this new fixator with electrical measurment, biomechanical experiment, photo-elastic and computer simulation three dimensional finite element analysis 13. Twenty wet copse adult humerus from a man dying of acute cranial brain injury were used to make fracture models. The fracture humerus was fixated with SMC surrounded by prescale to find out the stress of holding part and compression part. The stress range of holding part contacting with humerus was 2.42-22.68N, and the stress in the fracture surface produced by compression part was about 13.6 Mpa. Axial holding stress of SMC is 98.40N to 125.05N and longitidual dynamic compressive stress is 152~196N 16.

Principle of application

At a lower temperature after soaking in cold water, we could find transformation of SMC, then symmetrily put this fixator to fracture or nonunion site. Temperature drives transformation back and develop mechanics action: The memorial reverting stress of swan body, wing, neck develop axial express stress. The memorial reverting stress of swan neck develop axial stress at fracture or nonunion site. All the parts of SMC contribute to a three dimensional memorial fixation.

Surgical Technique

The nonunion site is exposed and debrided to healthy, bleeding, viable bone. Any synovial tissue at the nonunion site must be resected. The intramedullary canal also should be reestablished because it is an excellent source of osteoprogenitor cells. Putting SMC into the nonunion site to correct deformity and to obtain apposition of the bone ends. Liberal use of autogenous bone graft or another osteoinductive agent is imperative in atrophic, biologically inactive situations.

For SMC, sterility ice box and 500ml saline of 40-50℃ will be prepared. First, elastic transformation happened in 0 to 4℃ ice box and then we outspread swan wing, longer than fracture bone diameter, outspread swan neck as compression part and swan body collimating middle point to the fracture position, putting swan wing together back to fix the fracture stably. According to the position of swan claw we bore in cortical bone and insert the swan claw. SMC is reverting at 40 to 50℃ saline and fixation is finished.

Clinical application

From 1990 to 2001, complete records from 95 patients with nonunion of humeral shaft were reviewed and analyzed. Nine patients were excluded before analysis because they were lost to follow-up. In this study, no bilateral fractures were encountered, and nonunion was defined as failure to unite the fracture within 8 months of the initial injury. Among the 95 patients, there were 56 males and 39 females with an average age of 46.5 years (range from 17 to 71 years). The causes of initial injury were traffic accidents (n=65), falls (n=20), and direct contusion by miscellaneous materials (n=10). The initial state of injury showed that 45 fractures were of transverse type, 39 of oblique type, and 11 of comminuted type. Fifty-five were mid-shaft fractures, 22 distal-third fractures, and 18 proximal-third fractures. At the acute stage, 25 fractures were fixed conservatively, 25 with DCP alone, 27 with IM nailing, 12 with external fixation, and 6 with screws. Primary treatment were done at other institutions in all cases.

Radiographic evaluation of the nonunion found 57 fractures to be atrophic, and 20 to be hypertrophic, whereas 18 could not be defined clearly. The timing of treatment was an average of 9 months (range from 7 to 20 months) from the initial trauma. All patients received the same surgical protocol for treatment of the nonunion, consisting of removal of the previous implant (in patients with a previous implant in situ), decortication of the fracture site, refreshing the fracture site, recanalization of the intramedullary canal, reduction of the fracture, internal fixation with SMC, and application of a cancellous bone graft harvested form the ipsilateral anterior iliac crest. All procedures were done under general anesthesia by senior staff. All fractures were reduced as anatomically as possible. Arm slings were used and range-of-motion exercises were started immediately after the operation. Any labor with the injured limb was not allowed until the appearance of bridging callus or union. No other supplemental fixation, such as cast or brace, was used after operation. (typical case as Fig.3)

Figure 3. Preoperative plain radiograhps of a 50 year-old man with an nonunion of the humerus and radiograph of the same patient after appolication of a SMC internal fixation.

After the operation, each case was followed once every 2 weeks in the first month and once every month thereafter. Each patient had a special chart with a detailed record of personal data, mechanism and associated condition of the injury, type and classification of the fracture and nonunion, management course, condition and course of fracture healing, and functional recovery, until the final follow-up. An X-ray check-up was done at every follow-up visit, and all evaluations were done by senior staff. Normal union was defined as the appearance of bridging callus and partial obliteration of the fracture site within 5 months, delayed union as union evident in 6 to 8 months, and nonunion as no evidence of union in 8 months. Malunion was defined as varus or valgus deformity ≥15°,anterior or posterior angulation ≥15°, rotational deformity ≥15°, or shortening ≥15 mm, compared with the contralateral side. The follow-up period was an average of 38 months (range from 25 to 81 months).

Results :

All fractures united solidly, and thus, no case needed revision. The mean operation time was 107 minutes (range from 90 to 160 minutes), and the union time was 16 weeks (range 10-26 weeks). Based on preoperative and intraoperative findings, the causes of nonunion in these 95 fractures were soft-tissue interposition (n=25), poor reduction (n=26), inadequate fixation (n=15), secondary traumatic insult (n=10), multiple causes (n=10), and no significant cause (n=9).

The overall complication rate was 6.7 (7/95) in this series. Three episodes of superficial infection were noted 1, and all developed in the upper arm. All infections healed after debredement and antibiotic therapy. No deep infection developed in this series, transient sensory deficit of the radial nerve developed in 4 patients 1, all of whom had distal-third fractures. The injuries seemed to be neuroplaxia due to inappropriate stretch, and unrelated to the approach itself. All 4 patients recovered completely in 2 to 6 months without any functional impairment at the final follow-up visit.1No malunion was noted in this series.

All patients had satisfactory functional results, with neatly normal shoulder and elbow function, without noticeable pain, and a full return to pre-injury activities, without pain at the final follow-up visit.

Discussion :

The incidence of nonunion of the humeral shaft after operative and nonoperative treatment ranges between 0.3 and 2.5 percent, with the exception of two reports with 13 and 14 percent of nonunion of the humeral shaft after operative stabilization 14. There are no data on prospective trials of the treatment of humeral shaft nonunion. Most studies deal with their view of different surgical techniques, even in rather modest numbers. Studies on nonunion treatment best documented for compressive plate.

Compression plating of the humeral shaft has been said to cause stress shielding with compromise of the blood supply and a high incidence of radial nerve injury, especially with secondary interventions as nonunion repair after previous osteosynthesis.

Radial nerve injury after compression plating of the humeral shaft literature is reported as more than 10 percent 15, with other studies reporting less than 3 percent 20.In our opinion, an anteriolateral approach with routine identification and ample release of the radial nerve well beyond the nonunion ensures an acceptable rate of radial nerve injury. Preoperatively, several cases in our series had a combined medial and lateral positioning of plates, which devitalized the bone and obstructed union. There were only four cases of a transient sensory deficit of the radial nerve after surgery.

The mechanical and biologic features of the fracture and nonunion have a direct bearing on the optimal surgical treatment. Although a variety of techniques has been described, including locking intramedullary nails, unilateral external fixation, compression plate, the preferred treatment is SMC with the addition of autogenous iliac crest bone graft, and the success rate has been high. The indication for SMC can be as follows: upper limb diaphysis open or close transverse and comminuted fracture, upper limb diaphysis nonunion. The limit of SMC: the transformation variance of SMC is 8%,it’s the character of SMC, if break out, SMC will lose its memorial character.

In our opinion, SMC with frequent autogeneous bone grafting provide consolidation in one operation without serious complications. The advantages of this new internal fixed apparatus were as follows: one was the multi-point fixation which can enhance the stability, keeping the relative stability of the fracture or nonunion site at early stage, reducing the motion of the fracture and was good to bone healing. Second was persistent stable compression at the bone surface. Compression part can solve the stress shielding effect that existed at the routine steel plate fixation after the fracture line was absorbed and promote the healing of the late stage of the fracture or nonunion.

A point of consideration from bone healing character by SMC internal fixation: Two months after SMC fixation, fracture segment were replaced by “anatomic type”-plate bone. We consider that this bone healing phenomenon of no-solid no-micro, maybe have something related to the shape memory material and its dynamic stress or there maybe another unknown bone healing model?It even requires more explorations.

Reference :

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  2. Atalar AC, Kocaoglu M, Demirhan M, Bilsel K, Eralp L. Comparison of three different treatment modalities in the management of humeral shaft nonunions (plates, unilateral, and circular external fixators). J Orthop Trauma 2008;22:248-257.
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  6. Tomić S, Bumbasirević M, Lesić A, Mitković M, Atkinson HD. Ilizarov frame fixation without bone graft for atrophic humeral shaft nonunion: 28 patients with a minimum 2-year follow-up. J Orthop Trauma 2007;21:549-556.

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  13. Su jiacan,Cao honghai, Wang Ruiguan,Zhang Chuncai. Biomechanical feature measurement of Swan-like memory compression connector.Chinese Journal of Clinical Rehabilitation 2003; 20 :182-184.
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This is a peer reviewed paper 

Please cite as : Jia-can Su : Design And Clinical Application Of Swan-Like Memory Connector For Humeral Shaft Nonunion

J.Orthopaedics 2008;5(2)e16





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