Background: The primary aim of this study is to assess characteristics of pain in patients with ongoing pain after total knee arthroplasty (TKA). The secondary aim of this study is to identify specific pain patterns and link these to underlying pathologies. Methods: A prospectively collected cohort of 97 painful primary TKA patients was retrospectively evaluated. All patients followed a standardized diagnostic algorithm, which led to a diagnosis that set the indication for revision surgery. Character, location, dynamics, and radiation of pain were systematically assessed and correlated with the underlying pathologies. Results: Most frequent pain characters were pricking/lancinating (45.7%), pinching/crushing, and dull/ heavy (38.6%); 89.5% of all patients localized their knee pain anteriorly; 48.1% reported pain aggravations by descending stairs. Radiating pain was reported in 14% of the patients. Patella-related problems (56.7%) and instability (52.6%) were the most frequent pathologies. Based on correlations between the characteristics 6 specific pain patterns were identified. The most outstanding ones include the following: pattern 1, instability is associated with jumping/shooting, pricking/lancinating and tugging/wrenching pain, and aggravated by chair raising and starting; pattern 6, pain aggravation by descending stairs is associated with anterior and lateral jumping/shooting, tingling/stinging and sharp/lacerating pain character, and TKA positioning and patella baja. Conclusion:The assessment of painful TKA patients involving specific pain patterns help to further differentiate and define the clinical picture and ultimately the cause of a painful TKA. If the causes of the described complaints are known, a decision for a therapy can be made reliably and sustainably at an early stage before the state of pain becomes chronic.

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Purpose The diagnostic process in patients after painful total knee arthroplasty (TKA) is challenging. The more clinical and radiological information about a patient with pain after TKA is included in the assessment, the more reliable and sustainable the advice regarding TKA revision can be. The primary aim was to investigate the position of TKA components and evaluate bone tracer uptake (BTU) using pre-revision SPECT/CT and correlate these findings with previously published pain patterns in painful patients after TKA. Methods A prospectively collected cohort of 83 painful primary TKA patients was retrospectively evaluated. All patients followed a standardized diagnostic algorithm including 99m-Tc-HDP-SPECT/CT, which led to a diagnosis indicating revision surgery. Pain character, location, dynamics and radiation were systematically assessed as well as TKA component position in 3D-CT. BTU was anatomically localized and quantified using a validated localization scheme. Component positioning and BTU were correlated with pain characteristics using non-parametric Spearman correlations (p < 0.05). Results Based on Spearman’s rho, significant correlations were found between pain and patients characteristics and SPECT/CT findings resulting in nine specific patterns. The most outstanding ones include: Pattern 1: More flexion in the femoral component correlated with tender/splitting pain and patella-related pathologies. Pattern 3: More varus in the femoral component correlated with dull/heavy and tingling/stinging pain during descending stairs, unloading and long sitting in patients with high BMI and unresurfaced patella. Pattern 6: More posterior slope in the tibial component correlated with constant pain. Conclusion The results of this study help to place component positioning in the overall context of the "painful knee arthroplasty" including specific pain patterns. The findings further differentiate the clinical picture of a painful TKA. Knowing these patterns enables a prediction of the cause of the pain to be made as early as possible in the diagnostic process before the state of pain becomes chronic. Level of evidence Level III

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Aims and Objectives: About 20% of patients after total knee arthroplasty (TKA) are not satisfied nor pain free. After a challenging diagnostic workup it is not unusual that revision surgery becomes necessary. There is a general consensus that knee revision surgery should only be performed when the causes of the complaints are identified. In the clinical diagnostic process the detection of pain patterns that are typical for specific pathologies is paramount. Revision surgeons in clinical practice are well aware of some pain patterns but to date there is no study dealing with detection and identification of typical pain patterns in patients with painful TKA. The purpose of this study is the detection and definition of typical pain patterns in patients with painful TKA and the assignment to typical pathologies such as instability, stiffness, loosening, patellofemoral overstuffing and mechanical dysfunctions. Materials and Methods: A consecutive number of 129 patients, which were seen in the consultation at a specialized knee centre between 2012 and 2017 due to painful primary knee arthroplasty and whose diagnostic workup resulted in revision surgery were included. Defined criteria were retrospectively assessed from pre-existing patient documentation, statistic analysis (chi-squared test) and the assignment to the underlying pathology was performed. The criteria include localisation, intensity and character of pain, position and type of the prosthetic components, postoperative course, indication for revision surgery and demographic data such as age of the patient at primary surgery, sex, time between primary and revision surgery, socioeconomic status. Results: Typical pain patterns were defined and assigned to specific pathologies. Significant correlation was shown between localisation, intensity and character of pain and demographic data, type and position of the prosthetic components, surgical technique as well as the underlying cause for revision surgery such as instability, stiffness, loosening, patellofemoral overstuffing and mechanical dysfunction. Conclusion: The detection and definition of typical pain patterns in patients with pain after TKA and the assignment of identified pathologies will be applied in the improvement of the diagnostic process. Only when the exact cause of pain is determined, the therapy can be successful. The results of this study allow improving the clinical diagnostic process of patients with pain after TKA and help to enhance the indications for possible revision surgery.