PI
The most common type of PI was the PF impingement, in which cases the hypertrophied cyclops and synovium at the backside of the quadriceps tendon would contact with the distal edge of the trochlea creating mechanical irritation during knee extension. The fibrotic tissue were in discord with the femoral notch, which is substantially deeper in early PS design[23], thus this problem tend to occur more often in PS prosthesis. Other proposed technical risk factors consist of patella baja, smaller patellar components, increased posterior femoral offset, and flexed femoral components etc. [24]. The conservative treatment often was unsatisfactory[23], while most individuals with isolated PF impingement could expect an excellent result of arthroscopic resection[10] with low rate of recurrence[14]. These results were consistent with the present study. Another type was tethered patella syndrome. Adhesion and fibrous bands could be found from the inferior pole of the patellar component to the intercondylar notch, tethering the patella inferiorly[19]. Also the anterior border of tibial component or the insert post comes into conflict with hypertrophic soft tissue inside the intercondylar notch. It arises more in PS design as well[25]. Generally, the treatment was surgical removal of the irritating tissue. This often lead to good results too, which was consistent with the present study.
Anterior knee pain (AKP) was usually not specific, in such cases, crepitus could be found in history taking and/or physical exams, which could facilitate diagnosis. CT should be done to rule out obvious component malrotations which could lead to AKP as well. Intraoperatively, surgeons need to routinely check the existence of hypertrophic fibrous bands, synovium and potential impingement around the patella. Mild patellar maltracking might occur simultaneously due to block of the cyclops or tethering effect from the fibrous bands, normal patellar motion has to be checked in the end.
AF
In the present study, AF was the second largest subgroup. We defined a stiff TKA as a flexion under 90° and a flexion contracture over 10°. Treatment initiated with physical therapy. Manipulation under anaesthesia(MUA) could be feasible and applied in the later phase (at 6–12 weeks postoperatively), but may be related with risks of extensor mechanism rupture. Arthrolysis (open/arthroscopic) and revision surgery were options in refractory cases. In the current study, arthroscopic arthrolysis was always supplemented by MUA and CPM. Arthroscopy allows surgeon to release adhesions in a controlled manner. Previous investigations reported an average improvement in ROM of approximately 30° after arthroscopic release[15, 16]. Our results was similar. And it should be noted that the improvements in the current study, generated from both arthroscopic arthrolysis, MUA and intensive postoperative rehabilitation.
Even though detectable clinical or radiographic abnormalities had been already ruled out, six of twenty five patients encountered ROM limitation recurrence, five of them underwent a prosthesis revision. Frustratingly, we were unable to figure out risk factors for treatment failure due to a relatively small sample size, thus therapeutic efficacy for a specific patient with AF is less predictable. We suggest a delicate analysis of potential etiology. If apparent surgical errors are present, arthroscopy should be avoided. Arthroscopy might be helpful when the stiffness is caused by a tight posterior cruciate ligament(PCL)[15] or adhesions formation in the superior pouch or the medial and lateral retinaculum due to poor rehabilitation. Release of these tissue including the quadriceps and the PCL[15, 26] would enhance mobility. In contrast, extension deficit caused by a tight posterior capsule is not an ideal indication. Postoperatively, an intensive rehabilitation process with optimized pain control should be conducted to improve the outcome.
Synovitis
The etiology of synovitis after TKA is also multifactorial, which can be categorized into systemic, local and iatrogenic factors. Systemic factors include anticoagulant use or presence of a bleeding disorder. Local ones include trauma, inflamed synovium (eg, pigmented villonodular synovitis[27], crystalline and inflammatory arthropathies[28], and metal hypersensitivities[29]), or vascular anomaly (eg, arteriovenous malformation). Iatrogenic factors include an unrecognized vascular injury, implant malposition, loosening or knee instability[30]. Cases caused by vascular injury usually presents swelling within 6 months postoperatively[30]. There were no such cases in this study. Another more common mechanism and pathologic entity originates from hypertrophic synovium entrapment. Varied conditions could cause synovium hypertrophy, i.e. malaligned implants could lead to asymmetric PE wear and particle generation, causing synovial proliferation, subsequent impingement and bleeding. This is a more chronic process, usually occurring later than one year after TKA[30]. Four patients had wear induced synovitis in the current study.
Despite extensive case series, no consensus was made on how to provide best treatment. Conservative management consists of immobilization, cryotherapy, cessation of the anticoagulants, rest (and/or aspiration). But only thirty percents of the patients could had resolution[17]. Angiography and selective embolization offers another choice, with the advantages of low infection risk, ability to be performed under local anesthesia, and quick rehabilitation postoperatively[31]. It was reported to be effective in more than 90% of cases[32]. However repeat embolization may be necessary[33]. Also in patients with contraindications including severe renal impairment, contrast allergy, and difficult arterial access etc., arthroscopic synovectomy could be attempted. But unfortunately, the success is less predictable[17, 34, 35]. Previous research reported synovitis recurrence rate of 33%-50%[12, 17]. Additionally, the pathologic site was not always identified arthroscopically. These failure rates and intraoperative findings were in line with those in the current study. There is angiographic evidence of contrast “blush”, indicating the pathologic site, sometimes are arthroscopically inaccessible, i.e. at the posterior capsule[31]. In such circumstances, an open synovectomy is indicated which is often effective, with reported resolution of more than 90%[17, 36]. However infection risk, wound complications, and a prolonged rehabilitation would be of clinical concerns. Revision is needed when obvious clinical or radiographic abnormalities are present. According to the current patient cohort, arthroscopic synovectomy should not be the first line treatment for GS, good results were obtained in cases whose pathologic site could be identified and accessible arthroscopically and the etiology could be meanwhile dealt with.
In the current study, we utilized arthroscopy to manage PI, AF and GS. Keys for a good outcome incorporate precise diagnosis before surgery, systematic visualization of various compartment and careful procedure during arthroscopy, as well as rigorous and painless rehabilitation process. Avoiding unnecessary arthroscopic interventions in cases with clear technical errors is also important, as arthroscopy after TKA was associated with certain possibilities of recurrence, PJI and serious complications threatening patients' lives. Unlike other relevant studies[5], we did not include patients receiving arthroscopy for diagnostic purposes. The most important reason is that in this patient group, the sample size for different subgroups was rather low (less than ten), which would undermine statistical power[37]. From the clinical perspective, the application of arthroscopy as a diagnostic procedure could be avoided in some cases as it carries certain complication risks and in 8 patients in the current cohort, no pathology could be identified. And meanwhile recent literatures proposed new imaging tests to serve as appropriate and non-invasive diagnostic tools. In magnetic resonance(MR) imaging, frondlike hypertrophied synovitis was often found with PE wear, while in PJI cases, lamellated and hyperintense synovium could be discovered, in nonspecific synovitis, it often revealed as homogeneous effusion along with the signal intensity of fluid[38]. Also MR imaging could help distinguish qualitative differences in synovium appearance in TKA between particle-induced synovitis, infection, and nonspecific synovitis, with almost perfect interobserver and intraobserver reliability[38]. MR imaging had a 0.907–0.930 sensitivity and 0.723–0.738 specificity for a surgical diagnosis of complications related to polyethylene wear (including osteolysis and loosening); 0.652–0.783 sensitivity and 0.976–0.988 specificity for infection; and 0.643–0.667 sensitivity and 0.894–0.939 specificity for stiffness, instability, and nonspecific pain[38]. Other studies used MR angiography[39], synovial fluid cell phenotypes analysis[40], and SPECT/CT[41] etc. to help diagnose the etiology for painful TKA. These analysis had not been utilized in the present study. However they would be able to facilitate identifying the major etiology and prevent unnecessary arthroscopic examinations.
Several limitations should be acknowledged when drawing conclusions. The most important limitations include the retrospective study design, and the absence of a control group which can both lead to potential recall bias. Second, the study design would also induce selection bias. Third, the sample size in the PI and GS did not reach the number derived from the sample size calculations due to the particular patient population presenting to a single surgeon in a single center. And the lost to follow up rate was 19.6%, which poses a potential threat to the validity[42]. However the sample size in the current study was relatively large and the follow up duration was comparatively long. In the current study, we provided information and evidence on the therapeutic efficacy and safety of arthroscopic debridement to manage PI, AF and GS after TKA.