Monday, October 24, 2016

Too tight stem -> too high head -> rocking horse glenoid loosening

A stem that is tight in the diaphysis can result in a too high humeral component that can, in turn, lead to rocking horse loosening of the glenoid component as shown by the x-rays of the right shoulder below (middle aged man who presented to us with a painful stiff shoulder).

We revised this shoulder by removal of the loose glenoid component, smoothing the bony glenoid surface without bone grafting or glenoid component reimplantation and by replacing the humeral component with a smaller stem inserted at the desired height and fixed with impaction allografting.

A three months after surgery he has a comfortable, functional shoulder with radiographic evidence of glenoid healing and a centered humeral head in both the AP
and axillary views.

Comment: Impaction grafting of a small stem allows proper positioning of the stem. The management of a loose glenoid does not require bone grafting to fill the defect or reimplantation of a new glenoid component.


Rotator cuff sugery in patients over 75 years - is it worth it?

Rotator cuff surgery in patients older than 75 years with large and massive tears

These authors evaluated 64 elderly patients who underwent rotator cuff repair for large and massive rotator cuff tears. Repair was effected using a double mattress technique followed by a three month postoperative rehab program. An abduction brace was used for 7 to 8 weeks. The patients started passive forward elevation on the first postoperative day. After 4 weeks, pulley exercises to gain full forward elevation were started. Strengthening of the rotator cuff and periscapular muscle and wall pushups were started immediately after removal of the shoulder abduction brace at postoperative week 8. Posterior capsular stretching exercises and internal rotation stretching were initiated after approximately 3 months of strengthening exercises.

The mean postoperative follow-up period was 30.2 ± 5.2 months (range, 24-60 months). 80% were satisfied with their results. 26% had retears by MRI.

The authors concluded that "surgical treatment for large to massive rotator cuff tears in elderly patients with American Society of Anesthesiologists grade <4 provides good functional outcomes without morbidity, even in those with retears".

Comment: The results of patients with retears were essentially the same as those with intact repairs. The chart below compares the preoperative (pre) and postoperative (post) values for the intact and failed repairs.

It is interesting that the improvement in range of motion was better for those shoulders with failed repairs, as shown in the graph below that shows the change in the different parameters after surgery.

This study, like many before it, make us wonder about the indications and the benefit of a repair surgery with a prolonged rehabilitation program - especially in older individuals.

We find that many of these individuals are well served by a smooth and move procedure (see this link).


Sunday, October 23, 2016

Reverse total shoulder - managing glenoid bone defects

Reverse total shoulder arthroplasty with structural bone grafting of large glenoid defects

These authors point out that large glenoid defects pose difficulties in shoulder arthroplasty. They reviewed 44 patients (20 men and 24 women; mean age, 69 years) having a bulk structural graft behind the baseplate of a reverse total shoulder to manage structure defects.  The grafts consisted of a humeral head autograft in 29, iliac crest autograft in 1, or femoral head allograft in 14.

These cases used a prosthesis with a bone ingrowth stem on the baseplate

inserted over the bone graft as shown below.

Postoperative scores for the bone graft cohort were significantly lower than those in a cohort without grafting. Complete or partial incorporation was shown radiographically in 81% of grafts. 

Six baseplates were considered loose. The major (clinically significant) complication rate was 13.6%. There were 2 graft failures that caused clinical loosening of the baseplate and required revision. Two infections occurred (1 autograft and 1 allograft). One was revised in a 2-stage procedure, and 1 elected to retain the antibiotic spacer. One patient with clinical humeral loosening required revision (autograft). One postoperative dislocation (autograft) occurred. The patient was treated with a closed reduction in the operating room and immobilized for 6 weeks. No further dislocations occurred. Other minor (not clinically significant) complications included 6 patients with scapular notching of grades 1 or 2, and 4 patients with radiolucent lines of 2 mm around the humeral stem but without evidence of gross loosening. This resulted in a total complication rate of 36%.

Comment: There is no question that bone deficiency complicates shoulder arthroplasty. The question is when to use a graft and when to work with the bone stock available. That is a decision that can be made only by the operating surgeon based on the glenoid, the prosthesis used and the surgical technique.

We prefer to avoid structural grafts whenever possible because of uncertainty regarding quality, healing, and resistance to resorption. As pointed out in this paper, bone graft failures can cause clinical loosening of the baseplate.

Our preferred method for reverse total shoulder arthroplasty uses a central screw on the baseplate that provides immediate purchase in glenoid cortical bone without having to depend on bone ingrowth into a central peg and that provides lateral offset of the glenosphere to make up for bone deficiency.

In cases of glenoid bone deficiency, we use a small drill to probe the glenoid to find the appropriate area that offers the best bone stock.  The depth of solid bone is then verified with the tap: 30 mm is ideal.

The baseplate is then screwed into position, assuring that it locks securely in place when tightened.

Here is a recent case of failed shoulder hemiarthroplaty with severe glenoid deficiency.

Secure baseplate and glenosphere fixation was achieved by the method described.

This method may be considered instead of bone grafting when there is sufficient remaining bone of quality.

The challenge of diagnosing a propionibacterium "infection"

Optimal cultivation length to isolate Propionibacterium acnes in suspected bone and joint infections is > 7 days

JCM Accepted Manuscript Posted Online 12 October 2016
J. Clin. Microbiol. doi:10.1128/JCM.01435-16

These authors retrospectively studied whether reducing cultivation time to 7 days allowed accurate diagnosis without losing sensitivity. They identified patients with at least one positive P. acnes sample between 2005 and 2015 and grouped into ‘infection’ and ‘no infection’. They defined an ‘infection’ when at least two samples from the same case were positive. Clinical and microbiological data including time to positivity for different cultivation methods were recorded.

They identified 70 cases meeting their definition of  a P. acnes ‘infection’, in which 262 out of 379 samples were positive (69.1%). 47 cases did not fulfill our criteria for a proven ‘infection’ with only one positive sample (47 out of 215 samples, 21.9%). The most common sample site was shoulder (total n = 77), followed by hip (n=26). In the ‘infection’ group, they diagnosed PJI in 35 (50%) cases, and implant-associated infections with large (plates, intramedullary nail) or small implants (screws, anchors) in 10 (14.3%) and 17 (24.3%), respectively. Five cases presented with septic arthritis (arthroscopy-associated), and three cases with osteomyelitis (two in the shoulder after infiltration or trauma and one in the clavicula associated with b-cell lymphoma). In the ‘no infection’ group there were pain due to mechanical reasons in 22 (46.8%), aseptic loosening of an implant in 9 (19.2%), and
 other reasons in 16 (34%) cases diagnosed at revision surgery.

The cases of P. acnes "infection" had a significant faster median time to positivity of 6 days (range 2- 11 days) compared to 9 days in 47 cases with P. acnes identified as a contamination (p<0.0001).

 In 15 of 70 (21.4%) patients with an "infection", tissue samples were positive after day 7 and in 6 patients (8.6%) after day 10. Highest sensitivity was detected for thioglycolate broth (66.3%) and best positive predictive values for anaerobic agar plates (96.5%). A prolonged transportation time from the operating theatre to the microbiological laboratory did not influence time to positivity of P. acnes growth. By reducing the cultivation time to 7 days, false negative diagnosis would increase by 21.4%, thus they recommend culturing biopsies in suspected bone and joint infections to detect P. acnes for at least 10 days . They would have missed 6 cases (8.6%) if they had stopped cultures at day 10.

Their yield with sonication was lower than expected and they suggest the possibility that P. acnes might be inhibited or killed using ultrasound baths.

They conclude that a prolonged cultivation time is necessary for P. acnes  identification. They would have missed 21.4% of the P. acnes infections if cultivation time had been reduced to 7 days. Thioglycolate broth as an enrichment method for tissue samples showed a high sensitivity. The best positive predictive value was seen with direct incubation on anaerobic agar plates. Time to positivity of P. acnes growth  did not seem to be affected by a prolonged transportation time, which showed that P.  acnes in the biofilm of musculoskeletal infections can survive for hours even in a fastidious environment.

Comment:  This study effectively points out that longer incubation times result in a higher rate of culture positivity for Propionibacterium and the importance of anaerobic and broth cultures.

The definition of 'infection' as two or more positive cultures is, however, arbitrary due to the fact that Propionibacterium are not evenly distributed throughout the wound (see this link); whether or not a given specimen is culture positive depends on the 'luck of the draw'.

Rather than applying an arbitrary definition of 'infection' (and there are many), it would be clearer to report the number of specimens submitted from (a) tissue, (b) explant, and (c) fluid and the percent of each that was culture positive.

The bacterial load matters. Higher total numbers of bacteria in the wound will increase the percent of specimens that are culture positive, but a low percent of positive cultures does not mean the wound is aseptic.

We could take a number of samples of this lawn and not find two that show a mushroom, but that doesn't mean mushrooms are not really there.

Higher numbers of bacteria in a specimen will result in a shorter time to the recognition of a culture being positive, but a long time to positivity does not mean that the result is a 'contaminant'.

Consider the example below in which 1000 bacteria need to be present in order for the culture is recognized as positive. The red specimen contained 4 bacteria while the blue specimen contained one. The red specimen was 'culture positive' at nine days, while the blue specimen was interpreted as showing 'no growth' at 10 days.


Saturday, October 22, 2016

Metal backed glenoid components and failure rate.

The weak link in metal-backed glenoid implants is the polyethylene

These surgeons have authored a most thoughtful letter regarding the metal backed glenoid. We encourage reading of the complete letter (see this link) and their original article (see this link).

Here we paraphrase their letter. "the results this clinical study, showing poor results with metal backed (MB) glenoid implants at medium- to long-term follow-up, are in accordance with other long-term clinical studies reporting on a high number of patients and with a recent systematic review showing that the revision rate with MB glenoid components is 3 times higher than with all-PE components (see this link). Finally, biomechanics studies have demonstrated the problems created by the metallic interface in anatomic TSA on both the plastic side and the bone side. All these are good reasons, published in the literature, that do not encourage the use of MB glenoid components for anatomic TSA. Careful consideration of the inherent risks is warranted if future exploration of MB anatomic glenoid components is undertaken. The success of MB glenoid components for reverse TSA should not lead to confusion of surgeons: the biomechanical environment is very different in reverse TSA, in which a metallic sphere is associated to a metallic baseplate."

Comment: We have posted some informative links on this topic (see here, and here). In a recent post (see here) we point out that in addition to problems of thickness and back side wear, the issue is in large part the mismatch in the material properties of polyethylene and the metal backing.

Additional data on the difficulties associated with metal backed implants can be found from the robust database of the Australian Orthopaedic Association (see here), showing 'higher than anticipated rates of revision' for metal backed glenoid components.

Examples of these components are shown below:

While no prosthetic glenoid component is perfect, the current evidence is that the safest and most durable implants are the pegged all-polyethylene component

 inserted with careful and conservative glenoid bone preparation.


Systemic reaction after a Vancomycin spacer and systemic Vancomycin for treating a periprosthetic infection

Drug eruption secondary to vancomycin-laden spacer in the shoulder: a case report

These authors point out that periprosthetic joint infections (PJIs) after shoulder arthroplasty are often treated with two-stage revisions, involving prosthesis explantation, thorough d├ębridement, and implantation of an antibioticimpregnated cement spacer with a course of IV antibiotics followed by a revision arthroplasty. Antibiotic-impregnated cement spacers containing aminoglycosides or vancomycin are commonly used. Whereas the use of antibiotic spacers is generally considered safe, there have been previous reports of a diffuse desquamating rash from vancomycin-laden cement and cases of hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms after concurrent use of systemic vancomycin and vancomycin laden bone cement in the hip and knee. They report a case of a drug eruption caused by parenteral vancomycin in combination with a vancomycin-impregnated spacer inserted for a shoulder PJI.

The details of the case are interesting.  The patient was a 69-year-old with the diagnosis of rotator cuff arthropathy. He underwent a right reverse total shoulder arthroplasty in December 2012. In November 2014, the patient underwent a revision surgery to manage loose hardware and a broken baseplate screw. No culture specimens were taken at the time of the revision surgery.

The patient continued to have significant pain and was subsequently found to have a Propionibacterium infection diagnosed by aspiration. He then underwent an initial irrigation and d├ębridement with retention of implants and was prescribed a 60-day course of doxycycline.

Six weeks later, the patient was noted to have significant wound site drainage.

He was given a peripherally inserted central catheter line, through which he received multiple infusions of vancomycin 1000 mg during the course of 2 weeks without any adverse reactions. When that failed to eradicate the PJI, he underwent removal of the prosthesis with placement of a vancomycin-impregnated bone cement spacer; he also received vancomycin 1250 mg every 12 hours starting on postoperative day 1.

On postoperative day 4, he noticed swelling of his right arm, forearm, and hand. During the next 48 hours, he developed an erythematous, pruritic, maculopapular rash that spread to his entire torso and extremities.

These symptoms resolved after removal of the vancomycin spacer and a course of systemic steroids. 

Comment: Pharmacokinetic studies of vancomycin-loaded bone cement show that blood vancomycin levels reach peak blood concentration between 6 and 24 hours and fall to undetectable levels by the tenth day (see this link).

The point is that drug eruption reactions can occur after both systemic and local diffusion from antibiotic-laden cement spacers.


Humeral and glenoid component loosening - aseptic or culture positive? What can we learn?

Here are the films of the right shoulder of a man in his late 60s with glenohumeral arthritis

 and a posteriorly biconcave glenoid.

He had a total shoulder with mono block chrome-cobalt humeral component and a Hylamer glenoid.

He did very well after surgery, returning to gym workouts and a wide range of outdoor physical activities. His x-ray at three monte after surgery is shown below.

One year after surgery, he was still doing well. His X-ray at that time is shown below.

Seven years after surgery, his shoulder was becoming somewhat painful, but not so much that he wanted anything done. His x-rays at that time show glenoid component wear and humeral subsidence.

Thirteen years after his surgery, his symptoms were worsening as were the x-ray findings. He elected to give it a bit more time.

 Three months later the symptoms and x-ray changes (see below)

led to a revision surgery. Preoperative blood tests were normal.

At surgery the joint fluid was cloudy, but gram stains showed no neutrophils.

The humeral and glenoid components were loose and there was a thick humeral membrane. Frozen sections showed "Humeral membrane, right shoulder, excision: - Synovial tissue with extensive fibrosis and marked foreign body giant cell reaction with associated polarizable foreign material. - No neutrophils identified." 

The retrieved glenoid component showed substantial wear.

 Based on these findings, we considered the diagnosis of detritic synovitis (see this link).

He had a single stage revision to a hemiarthroplasty using Vancoymycin allograft for humeral fixation.

As a precaution we placed the patient on oral antibiotics (Augmentin) until the culture results were finalized.

In a week after surgery, the culture results came back as shown below

Note that the preoperative culture of his unprepared skin was strongly positive for Propionibacterium.
The humeral and glenoid explants and the membrane deep to the glenoid component were also strongly positive for Propionibacterium, while the humeral membrane specimens and joint fluid were unimpressive.
These findings emphasize that Propionibacterium is not uniformly distributed throughout the shoulder. Had the cultures been limited to the humeral membrane and joint fluid, the presence of Propionibacterium may have been overlooked.

With these culture results he was converted to the red protocol (see this link) of IV Ceftriaxone and Rifampin. 

Clinically, he is doing well with 140 degrees of assisted elevation and minimal shoulder discomfort.

Comment: This case is an excellent example of the complexities of the evaluation and management of a shoulder with delayed loosening of the total shoulder components. It is not possible to know if the Propionibacterium recovered from this shoulder were introduced from the patient's skin at the index surgery 13 years prior to the revision or if they arrived in the shoulder subsequently.

We have so much left to learn.