Neer Award 2017: A rapid method for detecting Propionibacterium acnes in surgical biopsy specimens from the shoulder

Background: Propionibacterium (P) acnes infection of the shoulder after arthroplasty is a common and serious complication. Current detection methods for P acnes involve anaerobic cultures that require pro- longed incubation periods (typically 7-14 days). We have developed a polymerase chain reaction (PCR)- restriction fragment length polymorphism (RFLP) approach that sensitively and specifically identifies P acnes in tissue specimens within a 24-hour period.
Methods: Primers were designed to amplify a unique region of the 16S rRNA gene in P acnes that con- tained a unique HaeIII restriction enzyme site. PCR and RFLP analyses were optimized to detect P acnes DNA in in vitro cultures and in arthroscopic surgical biopsy specimens from patients with P acnes infections. 
Results: A564base-pairPCRampliconwasderivedfromalloftheknownPacnesstrains.HaeIIIdigests of the amplicon yielded a restriction fragment pattern that was unique to P acnes. P acnes-specific amplicons were detected in as few as 10 bacterial cells and in clinical biopsy specimens of infected shoulder tissues. 
Conclusion: This PCR-RFLP assay combines the sensitivity of PCR with the specificity of RFLP mapping to identify P acnes in surgical isolates. The assay is robust and rapid, and a P acnes-positive tissue specimen can be confirmed within 24 hours of sampling, facilitating treatment decision making, targeted antibiotic therapy, and monitoring to minimize implant failure and revision surgery.
Level of evidence: Basic Science Study; Microbiologic Laboratory Study
© 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.

Comment: this is a significant contribution, the sample costs 5 dollars and it simplifies the process of diagnosis a low grade infection which most of the time is in "stealth mode" and it is difficult to diagnose. The protocol I follow when I suspect a p acnes infection is that I do a one stage exchange of the components, i do not remove well fixed components, I do extensive debridement and I prescribe oral Augmentin 875 mg BID for 14 days until the cultures are finalized. This window of antibiotic treatment with Augmentin can be eliminated with the use of this test. Below is an example of a different application for the diagnosis of pseudomonas.



The authors of the p acnes paper state:

"A major strength of PCR-RFLP assay described in this report is its specificity for P acnes. This specificity is predicted to be greater than routine culture-based approaches and previously published PCR approaches, because it has 2 levels of verification. The first level is PCR amplification with P acnes-specific primers, and the second is a P acnes-specific RFLP pattern. Previous reports had the first (albeit less specific than ours), but not the second. The strength of this extremely sensitive technology is the ability to detect fewer than 10 P acnes cells in the sample. The weakness is that this level of sensitivity makes aseptic sample collection very important. PCR and RFLP mapping are techniques that are routinely performed in many clinical microbiology and pathology laboratories, and so this approach is not restricted to highly specialized research laboratories."

Revision of failed cemented hemiarthroplasty to a reverse total shoulder replacement

Failure of healing of the tuberosities is considered a frequent cause of poor outcome after hemi-arthroplasty for proximal humerus fracture. Cemented hemi-arthroplasties that have failed to provide adequate pain relief or function to the shoulder are very challenging problems. Most of the time the patient is an elderly person, there might be associated osteopenia, and the active shoulder range of motion is limited. The following case is an example of the challenges that a surgeon is facing in the treatment of this complex problem.

This patient underwent 3 shoulder surgeries prior to referral to us.  The primary press fit hemi-arthroplasty for the proximal humerus fracture was the first surgery which was revised to a cemented hemi-arthroplasty due to loss of the version of the press fit prosthesis. The 3rd operation was done as an attempt to revise to a reverse shoulder replacement and a vascular injury resulted in abandoning the surgery. Subsequently the patient was referred to us for treatment. She had constant pain and very limited active forward flexion of the shoulder.

Below are the preoperative Grashey X-ray of the shoulder which demonstrates a high riding humeral head and prosthesis, failure of healing of the tuberosities, no signs of loosening of the implant, and thin cortices at the metaphyseal area of the proximal humerus. A CT scan shows good bone stock and no cavitation of the glenoid.

Revision to a reverse shoulder replacement was considered in this case as there was enough glenoid bone stock and the patient was older than 70 years of age. The main challenges of this surgery are outlined below:

1. Prior axillary artery repair, increase risk of repeat vascular injury as there is an altered surgical field from 3 prior surgeries

2. Although there is modularity of shoulder implants with the option to preserve the humeral stem and convert to a reverse total shoulder replacement, a high riding humeral prosthesis in combination with scar tissue from prior surgeries does not permit enough lengthening of the arm for conversion to a reverse.  

3. Preservation of the humeral stem seems impossible in this case as it is necessary to displace the humeral head distally enough to accommodate an inferior placed glenosphere on the glenoid

4. Removal of a well fixed cemented humeral stem in the setting of osteopenia with thin bone cortices  is one of the most challenging problems in shoulder revision surgery. There is a high risk for fracture.

Taking into consideration those challenges and being prepared for those complications we elected to proceed with conversion to a reverse total shoulder replacement. The steps for a conversion to a reverse are outlined below:

1. Careful approach to the shoulder using the previous deltopectoral approach

2. Removal of the prosthetic humeral head from the stem

3. Prior multiple cultures showed no signs of infection, however multiple cultures were obtained again

4. Osteotomes were used on the proximal collar to "debond" the prosthesis and avoid fracture of the tuberosities during the removal of the stem. 

 5. A vertical humeral uni-cortical osteotomy was performed with an oscillating saw. With a set of osteotomes that are placed vertically in the osteotomy site - within the osteotomy - gentle twisting opened the humeral envelope and increased the diameter of the canal by a few millimeters. Gentle repetition of this twisting created a visible gap between the cement mantle and the prosthesis. It is important to avoid distal extension of the osteotomy pass the tip of the humeral prosthesis as this creates a stress riser. 

6. A bone impactor is placed on the collar of the prosthesis proximally and the stem was gently tapped which resulted in extraction of the prosthesis.

7. Cables were passed around the shaft of the humerus and a new press fit implant was selected by assessing the diameter of the cemented humeral canal with a straight reamer. A "tight fit" is enough for fixation as later closure of the osteotomy site with the cables will create a stable construct. Cement can be used at this stage if desired.

The remaining part of the case was a typical implantation of a reverse prosthesis. 

Postoperative xray is shown below:

6 weeks after surgery there is healing of the osteotomy and no dislocation