Incidence of radius shortening following intramedullary nail fixation for gunshot fractures : a retrospective radiological audit

Intramedullary nail fixation is an option to manage highly comminuted fractures of the radius shaft resulting from gunshot wounds. However, complications including nail migration and malunion are well documented. We have noticed some patients presenting to our clinic with radiological shortening following nail fixation. This may result in chronic pain, reduced pronation and supination, poor grip strength and early onset arthrosis. This study aimed to quantify the incidence of radiological shortening following fixation of isolated gunshot wound (GSW) fractures of the radius with an intramedullary nail. Our secondary objectives were to identify if length of the zone of comminution and anatomical location of the fractures were risk factors for shortening, and to assess whether shortening was a result of surgical error, or whether shortening occurred over time.


Introduction
Fractures of the forearm resulting from gunshot wounds (GSW) are often highly comminuted, involving a sizable bone segment, and can be very challenging to treat. 1 The new generation locking intramedullary (IM) nail is an option to manage these highly comminuted fractures. 2,3 Minimal disruption to the soft tissue envelope together with its stress-shielding biomechanical properties makes the IM nail an attractive alternative to conventional bridge plate techniques. 4,5 The IM nail is not without its problems, and issues such as nail migration and malunion have been highlighted in the literature. 6,7 At our institution we have been using interlocking IM nails for isolated gunshot fractures of the radius since 2012. At follow-up we have noted some patients presenting with radius shortening following nail fixation to treat GSW fractures. Radius shortening is associated with clinical sequelae such as chronic pain, reduced pro-and supination, poor grip strength and early onset arthrosis of the distal radioulnar and radiocarpaljoints. [8][9][10][11] Our study aimed to quantify the incidence of radiological radius shortening following radius nails for GSW fractures at our institution. Our secondary objectives were to identify whether the radius was fixated in a shortened position or whether it shortened over time.
We also tried to identify any risk factors for radius shortening, specifically looking at whether length of the zone of comminution or anatomical location of the fractures contribute to its incidence.

Patients and methods
We performed a retrospective review of all (n = 40) isolated radius nails for GSW fractures performed at our institution between January 2012 and January 2019. We used the database from the nail provider (Afmed Pty Ltd) to confirm all cases were included in the study. Any radius nail with an ipsilateral fracture of the ulna that required fixation was excluded.
The latest AP forearm X-ray of each patient was assessed by two surgeons experienced in orthopaedic trauma. The rule of perpendiculars was used to calculate ulnar variance (UV) 12 ( Figure 1). All X-rays were assessed on our Philips Intellispace digital PACS (Philips, Netherlands). Shortening was defined in this study as a positive UV greater than 5.0 mm. If the radius was deemed to be short by consensus using this criterion, then the immediate postoperative X-ray was also assessed to gauge if the fracture was fixed short or if shortening developed over time. This X-ray was taken within 48 hours of surgery. All the cases where index X-rays were deemed not to be shortened were followed up radiologically to confirm that they remained outside the criteria for shortening stipulated in the study. No patients were found to cross over from the normal into the shortened category over the study period. Anatomical location (dividing radius shaft into thirds) and length of the zone of comminution in millimetres were assessed by two independent assessors (and a third in cases of disagreement).
The measurements were segregated into short and not-short groups. The distribution of the data was checked using the Shapiro-Wilk test. Normally distributed data were compared using student's t-test, and non-normally distributed data were compared using Mann-Whitney U test. Pearson chi-squared test and Fisher's exact test were appropriately used to find the dependence of shortening with the degree of fracture comminution and fracture location. The condition for statistical significance was set at p < 0.05. All the statistical analyses were performed using IBM SPSS v.26 (IBM Corp, Armonk, NY, USA).

Surgical technique
The procedure is performed with the patient supine on a radiolucent arm table, with the aid of a tourniquet. Prior to commencing the operation, the contralateral forearm is screened to pre-select the appropriate length and diameter of the nail, as well as to assess the patient's baseline UV in order to try replicate a similar UV on the affected side. There are three different length nails available (Acumed, USA), ranging from 190 to 230 mm. When deciding between two different lengths, we used the shorter of the two to avoid the possibility of a proud nail distally.
The entry point, just ulnar to Listers tubercle and 5 mm proximal to the articular surface, is found with the aid of fluoroscopy. A 1 cm dorsally based longitudinal incision is then made, and blunt dissection performed down to the bone, taking care to avoid injury to the extensor pollicus longus tendon or a small branch of the radial sensory nerve that may cross the surgical field. The near cortex is breached with the entry awl, paying careful attention to the AP and lateral direction of the awl. Inaccuracy of these initial steps, particularly in the AP plane, can result in a malreduction of the radius bow. Directing the awl in a slight radial direction can aid in avoiding   this error. The 3.1 mm reamer is then inserted into the medullary canal, the fracture reduced, and the reamer passed across the fracture, stopping at level of the biceps tuberosity. Depending on the ease of the pass, and the preoperative radiological assessment of the bone's canal diameter, the surgeon may choose to pass the 3.7 mm reamer to enlarge the medullary cavity to aid in the insertion of a larger calibre nail. The appropriately selected nail is then passed, making sure the fluted nail tip is seated firmly in the subchondral bone proximally to improve purchase. Tapping of the nail using a mallet is often needed to ensure adequate seating of the nail. Restoration of radius length is then achieved radiologically, and rotation confirmed using Evans rule, which states that the biceps tuberosity and radial styloid should be visualised 180° to one another in a normally rotated radius. 13 The nail is then locked with the forearm in supination, using a single dorsal 3.5 mm locking screw. Blunt dissection down to the bone is needed to avoid injury to important structures including the extensor tendons or a branch of the superficial radial sensory nerve. Careful intraoperative screening is needed post insertion to ensure the screw is not proud, as this may lead to extensor and flexor tendon irritation. An examination under fluoroscopy is performed to confirm whether the fixation is rotationally stable. If not, an above-elbow slab is used to limit pro-and supination, for a minimum of four weeks, or until soft callus is seen on X-ray.

Results
Forty patients met the criteria for inclusion in the study. No cases were excluded from analysis. Thirty-seven (93%) were male, with a mean age of 32.6 years (range 15-59). Twelve cases (30%) were assessed as radiologically short by both assessors. The mean shortening of the affected group was 7.4 mm (range 5.1-13.0). All 12 were deemed to have been fixed in a shortened position. One case was assessed to further shorten over time by approximately 2 mm.     Table I for a summary of results. We found no statistically significant (p = 0.55) difference between the average length of the zone of comminution (41.6 ± 25.9 mm in the shortened group and 35.6 ± 18.9 mm in the not-shortened group) and the incidence of shortening between the two groups.

Discussion
The surgical goals of any forearm shaft fracture fixation are the restoration of axial and rotational alignment, maintaining stability of the proximal and distal radioulnar joints and early range of motion. 1,3 For most forearm fractures, compression plating remains the gold standard, as anatomical reduction and primary bone healing are considered fundamental in achieving the best functional outcome. 3 Complications associated with plate fixation include a 0.8-2.3% risk of infection, 14 attributed to the extensive soft tissue dissection required, and up to 30% refracture rate when the plate is removed. 15 Fracture comminution however, a constant feature following GSW, 1 poses unique treatment challenges and precludes primary bone healing strategies in favour of secondary bone healing. Secondary bone healing can be achieved either by nonoperative means with the use of a plaster cast, or surgically, utilising either bridge plating techniques or IM nailing. Nonoperative management of adult diaphyseal radius fractures is associated with high complication rates, most notably failure to maintain reduction, radius shortening and stiffness. 5 The benefits of an intramedullary device over bridge plating include a smaller incision, improved cosmesis and less soft tissue dissection, while also maintaining a more optimal environment for healing due to minimal disruption to the fracture haematoma. 6,7 Its stress-sharing biomechanics also promote a predictably stronger fracture callus compared to bridge plating. 6 The early radial nails were criticised for their potential to result in iatrogenic injury to the posterior interosseus nerve during proximal locking. 6 This led to the development of the currently available radial nail, which has a flanged proximal end, eliminating the need for proximal locking while still providing rotational control through a press-fit mechanism into the unreamed subchondral bone. This requires attention to detail in the reaming step of the surgery (see surgical technique) as reaming beyond the bicipital tuberosity can potentially reduce the proximal purchase into the subchondral bone and therefore reduce the rotational control the nail provides. The modern nail is not without problems either, with nail migration and malunion (failure to restore radial bow) have been highlighted. 14 Many authors have investigated the clinical and biomechanical consequences of radius shortening. Crisco et al. reported that radius shortening changes the axis of rotation of the forearm, resulting in reduced joint congruency, reduction in rotation and changes in stress across the triangular fibrocartilage complex (TFCC). 16 Adams concluded that the greatest change in kinematics at the distal radius ulnar joint is due to radius shortening, which results in increased strain in the articular disc, and volar and dorsal radioulnar ligaments of the TFCC, leading to reduced grip strength. 17 They also reported that radius shortening results in changes in radiocarpal and radioulnar joints and that radius shortening has the most direct correlation with increased symptoms, including an increased risk of arthrosis. Lidstrom concluded their work by claiming that restoring radius length is the most important factor associated with a good clinical outcome. 18 Fernandez showed that radius shortening can result in reduced pro-and supination. 19 One of the patients in our series presented for her follow-up with significantly reduced supination, affecting her activities of daily living. Her postoperative X-rays show a positive ulnar variance of 11.7 mm (Figure 2). Comparative pictures shown in Figures 3 and 4 demonstrate her limitation in supination compared to the unaffected side. She underwent an ulnar shortening osteotomy ( Figure 5) to alleviate some of her symptoms. Figure  6 shows her improved clinical picture, six weeks post revision surgery. Distal radioulnar joint pain, ulnar impaction syndrome, TFCC tears and early onset osteoarthritis are the other commonly associated conditions attributed to radius shortening. 8,9,16 Ulnar variance (UV) is a commonly used radiological method to assess for radius shortening. Plain radiographs are proven to be acceptably accurate to measure UV. 10,12 Being a dynamic measurement, it is influenced by several factors including rotation, grip and beam direction, 20 and therefore, normal reference ranges differ. While international consensus on UV ranges is lacking, most quoted studies of UV in a neutral, relaxed position is 0.9 mm (range −4.1 mm to +2.3 mm). 10 To accommodate for magnification error, potential positional variability when taking the X-ray, and to allow for the potential of a patient having a pre-existing ulnar plus of up to 2.5 mm, we defined radiological shortening as more than or equal to 5 mm positive UV. We used the rule of perpendiculars to measure UV, having been shown to have the best interobserver reliability of the three commonly practiced methods of assessing. 10,12,21 There is ample published literature on the clinical impact of a positive UV. Most of the literature suggests that 2.5 mm is the amount of radius shortening beyond which clinical symptoms develop. [8][9][10]22,23 Early onset osteoarthritis due to increase in the mechanical load though the ulnar, 20 ulnar impaction syndrome, distal radius ulnar joint (DRUJ) pain/degeneration, reduced grip strength and carpal instability are also reported in the literature. 8,9,17,22 We could only find two articles that specifically looked at IM nails in the setting of GSW. In the first, the author makes mention of a case where DRUJ shortening occurs over the course of the healing process but does not elaborate further on its clinical significance. 7 The second paper is an outcome-based study and does not specifically look at radius shortening. 1 While formulating this study, we hypothesised that highly comminuted radius shaft fractures would shorten over time. We felt the mechanical properties of the IM nail may not be adequate to maintain length for sufficient time to allow union, as biomechanical studies have proven them inferior to plates. 5 The results of our study, however, seem to suggest that, should meticulous care be taken intraoperatively to restore the correct radius length before locking the nail, that shortening does not occur over time.
We therefore advocate the following steps to ensure shortening is avoided. First, take measurements of the contralateral radius for length and diameter in order to plan which available nail will give you the optimal proximal subchondral purchase, without leaving it proud distally. If only a single distal locking screw is available, inadequate purchase of the fluted blade tip into unreamed bone may render the nail length unstable. Pay careful attention to the relationship of the distal radius and ulnar of the unaffected side in order to reproduce it on the operated side. Intraoperatively, the authors feel that tapping in of the nail to get adequate subchondral purchase may inadvertently result in shortening. To mitigate this potential problem, one of our surgeons held the reduced DRUJ out to length before inserting the nail using a K-wire prior to the insertion of the nail (Figure 7). The wire was left in-situ for three weeks, and the patient healed in an acceptable position. Given what we now know about the nail's seemingly consistent ability to hold fractures out to length if acceptably reduced, we feel that removing the wire at the conclusion of the surgery, thus limiting the potential side effects of an in-situ wire, is appropriate. Lastly, we wish to stress the importance of screening for stability at the conclusion of the surgery, and if there is any doubt, liberal use of an above-elbow back slab for four weeks, or until soft callus seen on X-ray, is advocated.
The secondary outcome measures of the study aimed to determine if length of comminution or anatomical location of the fracture had any direct correlation with an increased incidence of shortening. While shortening was found to be dependent on the fracture position, with a predilection for the middle third of the radius, the length of the zone of fracture comminution was found to not be a significant contributing factor.
The study is enhanced by its relatively large sample size, given the sparsity of this surgery, but it is limited by its retrospective design. Being a retrospective review, we could not ensure all the X-rays were standardised, thus potentially affecting the dynamic nature of UV. As detailed in the discussion section, we attempted to overcome this by setting a relatively high positive UV as our cut-off to define shortening. Finally, we are aware of the limitations in our detection methods for identifying and defining radius shortening, due mainly to a lack of formal contralateral control X-rays showing the patients' baseline UV. Obtaining intraoperative radiographs upon completion of the surgeries would have removed the remote possibility that the fracture was fixed correctly and shortened in the immediate postoperative period. While screening the contralateral side is an important intraoperative step, its accuracy in UV measurements for the purposes of this study is insufficient.

Conclusion
The radius nail remains a useful tool to manage comminuted radius shaft fractures following GSW, yet careful attention to detail is needed intraoperatively to avoid radiological shortening, as seen in 30% of our case series. We found no evidence of subsequent shortening if the radius length is corrected before the nail is locked. We also did not find any causative relationship between length of the zone of fracture comminution and subsequent shortening but found a dependent relationship between fracture location and incidence of shortening.

Ethics statement
The authors declare that this submission is in accordance with the principles laid down by the Responsible Research Publication Position Statements as developed at the 2nd World Conference on Research Integrity in Singapore, 2010. Full ethics approval from the University of Cape Research Committee (HREC 580/2019) was obtained for this study. All procedures were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008.