Does preoperative abduction value affect functional outcome of combined muscle transfer and release procedures in obstetrical palsy patients with shoulder involvement?

Although the extent and severity of the deformity in obstetrical palsy may vary from patient to patient, shoulder is the most frequently affected joint. Many clinical and radiological classification systems had been described to address the problem and tailor the solution at the shoulder [1–5]. Among deformities affecting this joint, internal rotation contracture causing limitation of abduction and external rotation and dislocation of the shoulder is commonly observed on the follow up [4]. The shoulder instability was not caused directly by obstetrical trauma but related to a dynamic phenomenon of muscle imbalance. It was discovered that subscapularis muscle usually recovers more quickly than the external rotators and abductors [6, 7]. Despite initial conservative therapy, patients with partial recovery may develop internal rotation and adduction contractures at the shoulder. If this persists long enough, flattening of the humeral head and joint incongruence will ensue. Under these conditions the main goal of the treatment is to reestablish the muscle equilibrium. The first step is to treat the muscle release such as the posterior subscapularis slide or the modified anterior subscapularis tendon lengtening procedures. Afterwards, muscle transfer is performed to restore the missing external rotation and abduction function in patients with congruent glenohumeral joint and limited glenohumeral deformity. However external rotational humeral osteotomy is preferred in patients with similar external rotation weakness, internal rotation contracture but with severe glenohumeral deformity [1].

Usually release and transfer procedures are seperated depending on the age of the patient and condition of the shoulder but in older age group (>4 years), it is preferred to combine the shoulder release and muscle transfer simultaneously [6–8].

Some authors perform other muscle transfers like levator scapulae and trapezius along with latissimus dorsi and teres major only for total flail shoulders [9], others claim that if the preoperative abduction degree of the shoulder is less than 90° indicating a week deltoid and external rotator muscles, a trapezius muscle transfer must be added to latissimus dorsi and teres major transfers to achieve significant improvement of both abduction and external rotation [10].

In this study, we compared the results of combined release and tendon transfer operations performed at the same stage because of the late presentation of the cases, for shoulder abduction and external rotation in two groups of patients who did not have any surgical treatment before. In one group preoperative abduction degree was less than 90°, while in the other group it was equal or more than 90°. We compared the gains of abduction and external rotation in two groups and evaluated whether the preoperative abduction degree affects the functional outcome and in patients with preoperative abduction degree <90° and also another muscle transfer is needed along with latissimus dorsi and teres major transfers.

The average abduction degree improved from 62.5° (20°–85°) to 131.4° (90°–165°) and the average external rotation degree improved from 21.4° (0°–80°) to 82.6° (30°–95°) in Group I. We obtained 68.9° ± 22.9° (109%) gain for abduction and 61.1° ± 23° (285%) gain for external rotation. The difference between preoperative and postoperative values of abduction and external rotation was significant (ANOVA, F = 265 p = 0.000, F = 201 p = 0.000, respectively).

Although difference between preoperative abduction and abduction gain values in terms of degrees of Group I and Group II were significant (ANOVA, F= 43.1 p = 0.000 and F = 12 p = 0.001, respectively), the difference between postoperative values of both groups was insignificant (ANOVA, F = 1.257 p = 0.268).

There was also no significant difference between the preoperative external rotation, the external rotation gain and the postoperative external rotation for both groups (ANOVA, F = 2.017 p = 0.163, F = 1.848 p = 0.181 and F = 0.063 p = 0.803, respectively).

The results of both groups were shown in graphics in Figure 7.

Mean Mallet scores increased from 2.8 to 3.9 for global abduction, from 2.5 to 3.9 for global external rotation, from 2.1 to 3.6 for hand to head and from 2.5 to 3.5 for hand to mouth for Group I. Hand to back Mallet score decreased from 2.5 to 2.2. All the differences between preoperative and postoperative values were found significant according to the Student's t-test (t = -17.14 p = 0.000 for abduction score, t = -12.04 p = 0.000 for external rotation score, t = -13.06 p = 0.000 for hand to head score, t = 2.372 p = 0.023 for hand to back score and t = -7.361 p = 0.000 for hand to mouth score).

Mean Mallet scores increased from 3.5 to 4 for global abduction, from 2.8 to 4 for global external rotation, from 2.7 to 4 for hand to head and from 3.2 to 3.5 for hand to mouth for Group II. Hand to back Mallet score decreased from 2.8 to 2.1. All the differences, apart from hand to mouth score, between preoperative and postoperative values were found significant according to the Student's t-test (t = -2.53 p = 0.035 for abduction score, t = -3.592 p = 0.007 for external rotation score, t = -4.4 p = 0.002 for hand to head score and t = 2.8 p = 0.023 for hand to back score). The difference between preoperative and postoperative hand to mouth scores was found insignificant (t = -2, p = 0.081).

While the difference between preoperative Mallet scores of Group I and Group II concerning abduction, hand to head and hand to mouth was significant (ANOVA, F = 23.211 p = 0.000, F = 11.407 p = 0.002 and F = 7.692 p = 0.008, respectively), the difference was insignificant for external rotation and hand to back scores (ANOVA, F = 1.393 p = 0.244 and F = 2.475 p = 0.123, respectively). The difference between postoperative values of both groups was insignificant (ANOVA, F = 0.239 p = 0.627 for abduction, F = 0.76 p = 0.388 for external rotation, F = 2.764 p = 0.106 for hand to head, F = 0.354 p = 0.555 for hand to back and F = 0.363 p = 0.555 for hand to mouth).

Example cases from each group can be seen in Figure 8 and 9.

Internal rotation contracture is the most frequent and important secondary deformity of the shoulder in birth palsy. The problem is sometimes addressed by muscle release procedures such as the posterior subscapular slide or an anterior subscapularis tendon lenghtening operations. Once passive external rotation is improved, the child is later assessed for muscle transfers to reconstruct active external rotation if necessary [4].

According to Chang et al [5] there are two types of residual muscle impairment after recovery in the late obstetric brachial plexus palsy: motor recovery with cross-innervation and paralysis or paresis. Contractures of the pectoralis major, teres major, brachialis and biceps muscles, which are most frequently observed, cause the deformity of the shoulder and elbow. The reconstructive strategy include releasing of the antagonistic muscles (elongation of the pectoralis major and latissimus dorsi muscles) and augmentation of the paretic muscles (teres major transfer to the infraspinatus muscle for augmentation of shoulder external rotation and abduction and reinsertions of both ends of the clavicular part of the pectoralis major laterally for deltoid augmentation).

However, there are still many controversies concerning donor muscle choice for transfer, timing and operative tecniques of palliative surgical theraphy for the shoulder deformity.

The infraspinatus muscle works to center the humeral head in the glenoid throughout elevation. External rotation of the shoulder allows greater arm elevation by clearing the greater tuberosity from impingement by the coracoacromial arch. External rotation of the humerus also positions the long head biceps centrally to aid in its function as humeral stabilizer and loosens the inferior glenohumeral ligaments, thereby allowing greater arm elevation. Hence the infraspinatus muscle plays a key role in shoulder elevation as a humeral head stabilizer, an active abductor, and an external rotator of the shoulder [6].

The importance of transferring the teres major and latissimus dorsi as one conjoined tendon and anchoring into the posterior aspect of the greater tuberosity at the insertion of the infraspinatus similar to Hoffer method is augmentation of the weakened infraspinatus. Transfer with this technique instead of rerouting around humeral neck enables a stronger external rotator power because of the increased mechanical advantage at its insertion in the humeral head as opposed to the humeral shaft. The reason for the dramatic improvement of shoulder abduction after latissimus muscle transfer is probably because the transfer enhances the stabilizing effect of the rotator cuff which enables the deltoid to act more effectively, this phenomenon was called "force couple" effect by Phipps and Hoffer [11].

In many centers, muscle release procedures are performed before the age of two years, however for older children tendon transfer to restore abduction and external rotation is added [12]. It is accepted that the corrective procedures to rebuild the muscle equilibrium are best undertaken before permanent bony deformity occurs at 3 to 4 years of age [13].

Gilbert [14] suggested that release of the subscapularis is indicated if the external rotation does not improve more than 20°. Based on his 5 years of follow up, he reported excellent results after subscapularis release especially in patients before the age of 2 years. Raimondi also waits for the active external rotation due to the reinforcement of weak external rotator muscles after subscapular muscle release procedure in early ages but since recovery of the external rotators cannot be expected, he preferres the tendon transfer and muscle release operations at the same time in children older than 4 years of age [9].

Muhlig et al [12] described a common policy accepted by most of the centers. According to this; if passive external rotation of the shoulder stays < 30°, surgical treatment is indicated. If there is no posterior displacement of the humeral head than a subscapular slide will be used. However, if there is posterior displacement of the humeral head than subscapular lengthening by an anterior approach will be preferred. Indications for tendon transfer for improving external rotation and abduction are determined as well. If infraspinatus muscle does not show signs of reinnervation by the age of 2 years, a muscle transfer should be added to the subscapularis lengthening to avoid recurrence. If there is a fixed medial rotation contracture and posterior luxation of the humeral head with deformities of the glenoid than derotational osteotomy of the humerus should be added to the subscapularis lengthening.

As all of our patients were older than 2 years of age, we performed latissimus dorsi and teres major transfer at the same session with subscapularis and pectoralis major release.

In total flail shoulders, despite a certain degree of innervation, the functional results of shoulder corresponds to zero with the absence of a strong latissimus dorsi. In that condition, the levator scapulae muscle is utilised as an intrinsic stabilizer of glenohumeral joint and trapezius muscle is used as a prime mover for shoulder abduction with or without latissimus dorsi and teres major transfers [9].

Gilbert in his series of 44 patients with transfer of latissimus dorsi, the improvement of abduction was satisfactory in the shoulders which preoperatively coded as Grade III (Shoulder abduction is between 90°–120°, external rotation is between 0°–30°) or more, but not in those coded as Grade II (Shoulder abduction is between 45°–90°, external rotation is to neutral) or less. Hence he thought it may be necessary to add a concomitant transfer of the trapezius to the patients whose abduction of the shoulder was weak or absent [15].

Chen et al [10] asserted the need for an additional trapezius muscle transfer for shoulder of the patients who had less than 90° abduction to increase the success of the classic latissimus dorsi + teres major transfer. They transferred latissimus dorsi by fixing its tendon to the insertion of the infraspinatus and tenotomized the teres major and then attached to the belly of the latissimus dorsi and found out in their early stage of treatment that, 10 of 18 cases with abduction less than 90°, with transfer of the latissimus dorsi and the teres major, patients gained no improvement of abduction but some recovery of external rotation, while five of seven patients with abduction equal or more than 90°, made significant progress in both abduction and external rotation.

Al-Qattan [16] performed latissimus dorsi transfer on 12 children with variable preoperative shoulder abduction (range 60–150°, mean 100°) and postoperatively ten children achieved a modified Mallet score of 4 and were able to reach the occiput easily and they had mean 140° active shoulder abduction (range 90–170°). Hence the author also did not find any difference in patients with weak or strong preoperative abduction.

It is our opinion that in our Group I patients, the co-contraction between shoulder abductors (supraspinatus, infraspinatus and deltoid) and adductors (mainly, pectoralis major, teres major and latissimus dorsi) and also subscapularis muscle tightness cause limitation of shoulder elevation. If antagonistic muscles (teres major and latissimus dorsi) are transferred for the paretic muscles (infraspinatus) and the pectoralis major and subscapularis muscles are released with preserving their shoulder stability function, these children can have as succesfull postoperative shoulder abduction and external rotation as the children in Group II, who has less cross innervation hence better preoperative abduction value. Group I and II patient had almost similar postoperative mean abduction (131.4° & 140°, respectively) and external rotation values (82.6° & 82.7°, respectively).

Extensive dissection of latissimus dorsi and teres major muscles from the surrounding structures gave us the opportunity to utilize both muscles for transfer, without any difficulty during the passage of the conjoined tendon through the tunnel which was prepared between long head of triceps and deltoid muscle, and also during reinsertion to the humerus.

Several authors reported recurrences of the deformity in terms of reduction of external rotation and abduction gain. Two of the 12 children in Al-Qattan series [16] and three of 35 cases in Phipps and Hoffer series [11] had recurrence of the deformity. Al-Qattan [16] classified the possible cause of this late complication as recurrence of the internal rotation contracture (mainly in the subscapularis), gradual contracture of the teres major as part of the inferior glenohumeral angle contracture and co-contraction of the muscles. We did not have any recurrence of the deformity during the follow-up period which may be related to the use of rigid fixation with bone anchors for reinsertion of the conjoint tendon.

We believe that in cases who has congruent glenohumeral joint (Type I-III Waters-Peljovich grading system), and deltoid muscle strength of M3–M4 (British Medical Research Council evaluation) but weak or absent external rotation, if the latissimus dorsi and teres major muscles have sufficient strength (M3 or more), the ideal procedure is transfer of latissimus dorsi and /or teres major onto the posterior aspect of the greater tuberosity of humerus, at the insertion of the infraspinatus. So we are not totally convinced about adding trapezius muscle transfer concomitantly with the latissimus dorsi + teres major transfer session. We rather preserve this muscle for the patients that could not achieve enough shoulder abduction after the first operation.

Since our study was not randomised to treatment, the groups did not comprise equal number of patients, the assessments were not performed by independent observers but by a physiotherapy group of our team at postoperative 24 – 60 months (not at the same time for everyone), we would like to interpret our conclusions cautiously.

Almost near normal shoulder function can still be reached in children who could not receive primary early neural reconstruction, by combined muscle release and muscle transfer operations which are performed before the severe glenohumeral deformities occur.

We found out that the patients with obstetric palsy shoulder sequela who had a preoperative abduction value less than 90° could have good functional results as the patients who had preoperative abduction values equal or more than 90°, with latissimus dorsi, teres major muscle transfer and subscapularis muscle release.