Prevalence and etiology of elbow flexion contractures in brachial plexus birth injury: A scoping review

Early conjectures on the etiology of elbow flexion contractures described osseous changes to the elbow following immobilization of the elbow in a flexed position after BPBI in infancy (Table 3) [33, 42, 49]. However, splinting was not the only therapy intervention implicated in elbow flexion contracture development. Elbow dislocation associated with using the elbow as leverage during forceful passive range of motion exercises to counteract an internal rotation contracture at the shoulder was discussed in early reports where the resultant dislocation was presumed to cause an elbow flexion contracture [37].

After these initial reports, Ballinger and Hoffer [19]. conducted a study in 1994 that found that 85% of elbow extensors were at least one muscle grade (Medical Research Council scale) stronger than the elbow flexors in 34 children with C5–C6 injury who had elbow flexion contractures (Table 3). This provided evidence that muscle imbalance alone cannot fully explain the development of these contractures. However, imbalance in muscle strength may still be a factor, especially in cases of specific BPBI lesions that result in flexor dominance over extensors [36]. For example, in a total plexus injury with severe insult to C7, the elbow extensors may experience marked weakness compared to elbow flexors [17, 36, 59].

Since Ballinger and Hoffer [19] highlighted the paradox of elbow flexion contractures, the number of publications on elbow flexion contractures have increased (Fig. 3). Indeed, ten of the 12 studies reviewed were published after Ballinger and Hoffer’s study. The evidence from studies with the specific objective of determining etiological factors associated with elbow flexion contractures is summarized in Table 3. The majority of the evidence was based on anecdotal evidence from clinical observations. Several potential etiological factors reported based on expert opinion and clinical observations include: flexor domination over extensors due to earlier timing of reinnervation of flexors [19], elbow flexor training effect from therapeutic expectations or positioning preferences [9, 17, 18, 19, 54, 55, 60], fibrosis in muscle after birth trauma [20, 31, 35, 46], co-contraction of elbow flexors and extensors [1, 9, 14, 41, 43, 52, 61], and developmental motor apraxia [51]. There was one observational study that showed that overactivity of the long-head of the biceps brachii muscle is an associated factor in elbow flexion contractures [21]. The remaining studies investigated the characteristics of the elbow flexor muscles in BPBI. This includes five murine model studies.

Clinical evidence from imaging (CT, MRI) and murine models provide supportive evidence that elbow flexion contractures develop as a result of denervation in the upper limb muscles in the neonatal period (Table 3) [3, 62]. Injury to the brachial plexus outside the neonatal period may not necessarily result in such a contracture [3]. More specifically, the denervation process negatively affects the biceps brachii and brachialis muscles as demonstrated by evidence of fatty infiltrations, shortened length, and decreased cross-sectional area [3, 22, 31, 44, 56, 58].

Afferent innervation preservation has the potential to provide a protective effect on the denervated muscles by preserving muscle spindles through ErbB signaling activity [24]. Brachialis pathology was more significant than the biceps in both clinical and animal studies [23, 44]. Fibrosis of these muscles also occurs, but in the later stages of the contracture [23].

9. Implications of an elbow flexion contracture

The negative functional and aesthetic impact of these contractures due to the inability to achieve full elbow extension and the exaggerated limb length discrepancy was mentioned in many reports [1, 2, 3, 5, 9, 11, 12, 13, 16, 17, 21, 38, 41, 47, 50, 52, 60] Five studies provided a descriptive non-standardized account of the child’s and family’s concerns [2, 9, 13, 21, 47]. One study surveyed the opinion of surgeons who provide care to children with BPBI, and found that 50% of those polled viewed an elbow flexion contracture as a problem when the contracture is $>$ 45 degrees [63]. The remaining reports were based on expert opinion, with the exception of one study that used standardized measures of upper extremity function [21]. In that study, Sheffler et al. found that children with elbow flexion contractures secondary to BPBI scored below normal on the upper extremity function scale of the Pediatric Outcomes Data Collection Instrument (PODCI), while their elbow specific function was 6.4 out of 10 on the Liverpool Elbow Score and 82.9 (good) on the Mayo Elbow Performance Score [21].

10. Discussion

The collective clinical experience from this review indicates that elbow flexion contractures are a common sequela of BPBI that affects, on average, half of children with BPBI who have an incomplete neurological recovery. However, issues of both over and under-estimation of the prevalence are associated with the studies reviewed. An overestimation of the prevalence may occur because the children in these studies were more likely to have more severe injuries due to sampling from a clinic setting. Conversely, the retrospective nature of the six of seven studies reviewed relied on documentation of health care professionals on the presence and magnitude of these contractures in a clinical setting. Underreporting of contractures may be experienced due to errors of omission by attending clinicians in documentation or if the presence of a mild contracture was missed.

The majority of elbow flexion contractures are mild, but approximately a third of children with a contracture will have an extension deficit of 30 degrees or greater. When the contracture reaches this severity, theoretically it can have a negative impact on the child’s function during activities of daily living [4]. However, this review found that rigorous evidence on the functional and aesthetic impact of elbow flexion contractures secondary to BPBI is lacking. There is a gap in the literature on the activity limitation and participation restrictions caused by this impairment from the perspective of those with this impairment. Sheffler et al.’s study is helpful in highlighting some of the concerns with evaluating the functional and aesthetic impact of these contractures [21]. They reported that children with elbow flexion contractures secondary to BPBI had below normal performance on the PODCI upper extremity scale. However, it is difficult to isolate the effect of the elbow on overall arm function. A valid method of evaluating the functional and aesthetic impact of the elbow flexion contracture is difficult when the appearance, as well as motor and sensory function of the entire limb is affected after a BPBI. Elbow specific tools may be helpful, however most assessments of the elbow are not designed for this population.

This review found that elbow flexion contractures gradually progress during childhood. Sheffler et al. found a progression at 4.4% per year in patients prior to receiving conservative treatment [1]. However, it is important to consider, as stated by the authors themselves, that those who seek treatment are more likely to have more severe contractures. Further, it is unclear from this average rate what proportion of children did not progress at all. From their study, one can appreciate the difference in the progression of mild contractures, as those who did not seek treatment progressed 0.1% annually. However, identifying and directly studying those whose contractures do not progress at all is an important step to understanding the etiology and nature of this condition.

Therapeutic interventions may play a role in the presence and progression of this contracture. The historical evidence from this review demonstrated that using a splint to immobilize the elbow joint in flexion can lead to an elbow flexion contracture. This lesson was shown to be still relevant, as a report of an elbow flexion contracture after splint immobilization surfaced in 2014 with the use of the pilot version of the sup-ER splint [49].

Postural preferences may also play a role in elbow contracture development and persistence. Elbow flexion posturing may be advantageous for children with BPBI as a compensatory strategy to optimize upper extremity function. It can provide stability for gripping and manipulative activities in the presence of instability or weakness at the shoulder or wrist joints. As electromyographic evidence suggests, the elbow flexors may also be overworking as a means of stabilizing the shoulder [2, 21, 33]. Elbow flexion contractures associated with a shoulder internal rotation contracture may also contribute to the posturing of the elbow. Al-Qattan found a reduction in the degree of elbow flexion contracture after surgical correction of a shoulder internal rotation contracture with a derotational osteotomy of the humerus [9, 52, 60]. He postulated that the internally rotated position of the shoulder results in a compensatory abduction of the shoulder in order to optimize function of the limb. As a result, there is a preference to posture the elbow in slight flexion with the hand resting naturally in front of the body [60].

Lastly, this review clearly illustrates the evolution in the understanding of the etiology of elbow flexion contractures from anecdotal clinical observations to objective evidence from medical imaging and laboratory science. Evidence from murine models has advanced our understanding of the physiological causes of elbow flexion contractures and potential avenues to remediate this problem. There is clear evidence that muscle imbalance and fibrosis in the flexor muscles are not primary contributors to this problem. The evidence points towards the physiological response of muscle denervation that results in the failure of growth in the sarcomeres of the flexor muscles. More specifically, denervation results in loss of ErbB signaling in the muscle spindles. Interventions to improve the rate of reinnervation after injury or prevent denervation effects may help prevent the development of these contractures. Nikolaou et al. explored the effects of preserving afferent innervation to the muscle spindle in order to preserve muscle spindles and longitudinal growth of affected muscles [24]. Their findings offer direction towards exploring the potential of ErbB signal modulation as a mechanism to prevent the development of elbow flexion contractures after BPBI. It also spurs the need for clinical research to explore the effects of early reinnervation on the occurrence of elbow flexion contractures.

In summary, this scoping review identified that approximately 50% of children with residual impairment after a BPBI are affected by an elbow flexion contracture. The etiology of these contractures is multifaceted. Muscle imbalance does not play the primary role in these contractures, although it may still affect children with BPBI lesions who recover with significant weakness in elbow extensors. Similarly, splint positioning, postural preferences, and level of activity that uses the elbow through its full range of motion may play a small role in the occurrence, severity, and progression of contractures. However, the best evidence to date on the primary etiology of these contractures is that denervation of the elbow flexors in the neonatal period causes physiological changes that negatively impact muscle growth. Further investigations at a physiological level to study the changes to the implicated brachialis and biceps brachii muscles may help further our quest to remediate this problem.