Complications and Outcomes of Minimally Invasive Percutaneous Plating for Proximal Humeral Fractures

We retrospectively reviewed the medical records of 21 consecutive patients with displaced proximal humeral fractures. The study was approved by the Institutional Review Board. These patients were treated from March 2009 to March 2011 using the MIPO technique with periarticular proximal humeral locking plates (Zimmer, Warsaw, IN, USA). A minimum of one-year of follow-up data were evaluated for each patient. There were 1 male and 20 female patients with an average age of 61 years (range, 16 to 82 years).

The Neer and Orthopedic Trauma Association (OTA) classifications were used to characterize the fracture patterns (Table 1). Regardless of varus-valgus fracture type, only 2-part surgical neck fractures and 3-part fractures with displacement10) (> 1 cm or > 45°) were included in this study, because we believe that such fractures are amenable to reduction by minimally invasive percutaneous techniques. The fractures including lesser tuberosity fragments were excluded, because indirect reduction and internal fixation of such fragments are difficult using a direct lateral approach without damaging the anterior humeral circumflex artery.5, 9) However, the reduction and internal fixation of the greater tuberosity fragments may be facilitated through proximal incisions of the direct lateral approach.5) Four-part fractures and articular surface fractures, such as head-splitting or impression fractures, were excluded. The patients with neurological symptoms in the injured upper extremity were also excluded to avoid selection bias. In short, our inclusion criteria were by fracture types, which only included the displaced 2-part surgical neck fractures and 3-part fractures, without the lesser tuberosity fracture and the neurological symptoms.

Table 1
Summary of Cases

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The same surgeon (JP) performed all of the interventions using the MIPO technique and the periarticular anatomical locking plates. The postoperative follow-ups were conducted monthly for the first three months, and the radiographs were taken at each follow-up clinic visit. After the initial three months of follow-up, all patients were followed every three months. If there was no evidence of progression to union by the third month, the patients returned at one-month intervals for the radiographic confirmation of union. The mean follow-up duration was 20.8 months (range, 12 to 24 months). The radiographic union and the active range of motion were assessed at each follow-up, and the Constant scores were measured at 3, 6, and 12 months postoperatively. The radiographic union was defined by bridging callus formation in at least three cortices on the radiographs made in two orthogonal projections.16, 17, 18) We defined the clinical union as an absence of tenderness or pain on the fracture site at rest.

The average shoulder flexions at 3 month, 6 month, and 1 year follow-ups were 91.4° (range, 50° to 140°), 116.7° (range, 80° to 160°), and 133.3° (range, 80° to 170°), respectively. The average shoulder abductions at 3 month, 6 month, and 1 year follow-ups were 70.5° (range, 40° to 130°), 104.3° (range, 80° to 150°), and 121.9° (range, 90° to 160°), respectively. The mean Constant scores at 3 month, 6 month, and 1 year follow-ups were 74.0 (range, 62 to 90), 79.4 (range, 64 to 91), and 82.7 (range, 66 to 92), respectively (Table 1).

All the patients demonstrated osseous union within the average of 3.2 months (range, 2 to 6 months). There was one case of a delayed union with a bone defect around the lateral cortex just below the surgical neck with proximal screw loosening. This defect spontaneously filled by six months postoperatively (Fig. 1). The proximal screw loosening (an approximately 5-mm back-out) showed no further problematic movement. There was another case of the screw penetration into the glenohumeral joint that was detected at the first follow-up. However, it was left in place because the patient strongly refused additional surgery. The intra-articular screw perforation remained unchanged on the one-year postoperative radiographs. Any plate failures or inadvertent neurovascular injuries were not observed during the study period. There was one patient presenting with the slight deltoid muscle atrophy, the abductor weakness (grade 3, active movement against gravity) without sensory deficit, and the limited range of motion (11th case in Table 1). The axillary nerve paresis was diagnosed in this patient six months postoperatively, using the electromyography (EMG) and the nerve conduction velocity studies (NCS). The motor NCS showed that the injured axillary nerve had almost half of the normal amplitude compared to the uninjured axillary nerve. EMG and NCS performed at one year postoperatively demonstrated little interval change of axillary nerve paresis (Fig. 2). However, deltoid muscle atrophy disappeared, abductor weakness improved (grade 4, active movement against resistance), and the patient was able to flex and abduct the shoulder to 90° one year postoperatively (Table 1).

Fig. 1
(A) Proximal humeral fracture. (B) After internal fixation using minimally invasive plate osteosynthesis, a lateral cortical defect (arrow) near the surgical neck was observed on the immediate postoperative radiograph. (C) However, this defect spontaneously disappeared on a radiograph taken six months postoperatively.

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Fig. 2
Electromyography and nerve conduction velocity studies (NCS) performed one year postoperatively showed that the amplitude of the injured right (Rt) axillary nerve (A) was almost half of the normal amplitude of the uninjured left (Lt) axillary nerve (B). EP: evoked potential.

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No cases of AVN of the humeral head were seen including the last follow-up. There were no cases of rotator cuff tendon injury during the procedures. No cases of impingement syndrome between the plate tip and the acromion, due to deep insertion of the plate, were observed. No hardware removal and no secondary operations were performed during the study period.

Even though conservative, nonsurgical treatment is the mainstay for the proximal humeral fracture,1, 2, 3) it requires a great deal of the patient compliance. For minority of the patients who require surgical treatment, several options are possible. These options include percutaneous pin fixation, open plating through a deltopectoral approach, antegrade humeral nailing, and humeral head replacement.19, 20, 21, 22)

Advances in the locking plate systems and the rise of biological fixation concepts have changed many surgeons' approaches to the fracture treatments. Since plating with the MIPO technique preserves the blood supply, unlike the open plating which requires periosteal stripping, the MIPO technique is gaining its popularity.9)

The anatomical locking plate systems facilitate plating with the MIPO technique, and they eliminate the need for plate precontouring. Moreover, when the proximal locking screws are cannulated, as in the periarticular proximal humeral locking plates (Zimmer), the screws can be inserted into the metaphyseal region of the proximal humerus along the guide wire without losing a predrilled path.

The advantages of the MIPO technique include the higher union rates, decreased need for bone grafting, lower AVN rates, and fast functional recovery.5, 10, 11, 12, 13) In this study, bony union was achieved in all of the patients, even in those with the osteoporotic fractures. One case of a delayed union (Fig. 1) with a bone defect was eventually filled without the bone grafting at 6 months postoperatively.

The complications associated with the minimally invasive plating for proximal humerus fractures include the intra-articular screw penetration, proximal screw loosening, plate failure, and AVN of the humeral head.10, 11, 12, 13) Although there have been a few studies14, 15) reporting axillary nerve paresis due to the MIPO technique for the treatment of proximal humeral fractures, the axillary nerve paresis was only briefly mentioned without any detailed description. We want to report one case of an axillary nerve paresis in more detail. This paresis was confirmed with EMG and NCS at 6 months postoperatively, and was compared to the same test at one year postoperatively. There were little interval changes between the two consecutive EMG and NCSs.

One cadaver study reported that the axillary nerve can be elevated by an average of 13.4 mm from the bone without becoming taut.8) However, in the clinical practices, even more elevation, or traction of the soft tissue envelope around the fracture zone, may be necessary during the indirect fracture reduction or the screw insertion near the fracture zone. The axillary nerve paresis in this study might have resulted from the intraoperative traction of the axillary nerve during the insertion of proximal locking screws, because there were no cases of inadvertent nerve injuries during the operations and the patients with neurological symptoms in the injured upper limbs were excluded from this study. Therefore, when assessing the risk-benefit ratio for the minimally invasive percutaneous plating of the proximal humeral fractures, the possibility of traction injury of the axillary nerve should be considered along with the complications mentioned above. The young patients with tight, soft tissue tensions may be more susceptible to such injuries, even though the traction injuries are usually incomplete.

No cases of AVN of the humeral head were seen in this series, perhaps because of the anterior humeral circumflex artery and its ascending branches being uninjured due to the exclusion of lesser tuberosity fractures.

The main limitation of this study is the small number of patients included in the sample. However, we believe that our report will contribute to the body of literature on the possibility of axillary nerve paresis during the minimally invasive plating for the proximal humeral fractures in the clinical practices. Prospective, large-scaled, controlled trials with EMG and NCS are needed in the future for better objective evaluation of the axillary nerve paresis with the MIPO technique as the treatment for proximal humeral fractures.

In conclusion, the minimally invasive percutaneous plating using the periarticular locking plates is a useful option for the selected patients with displaced proximal humeral fractures. The MIPO technique provides fast union, good functional recovery, and decreased need for bone grafting. However, when selecting the patients for minimally invasive platings, clinicians must consider not only the implant related complications of screw loosening and intra-articular screw perforation, but also the possibility of axillary nerve paresis.